One bottle labelled as zinzib. R. pulv., full; ditto, spirit. rect., empty; ditto, mur. hydrarg. seven-eighths full; ditto, ol. caryphyll., one-fifth full; ditto, ipec. P. co., full; ditto, ol. menth. pip., empty; ditto, liq. ammon. fort., three-quarters full; ditto, ol. olivac., full; ditto, tinct. opii. camph., three-quarters full; ditto, vin. sem. colch., full; ditto, quarter full; ditto, calomel, full (broken); ditto, hydrarg. hit. oxyd., full; ditto, pulv. gregor, full (broken); ditto, magnes. carb., full; ditto, camphor, full; two bottles tinc. tolut., each quarter full; one bottle ipec. R. pulv., full; ditto, jalap R. pulv., full; ditto, scammon. pulv., full; ditto, quinac bisulph., empty; ditto (not labelled), tinct. opii., three-quarters full; one box (apparently) purgative pills, full; ditto, ointment, shrunk; ditto, emp. adhesiv., full; one probang, one pen wrapped up in lint, one lead pencil, one pewter syringe, two small tubes (test) wrapped up in lint, one farthing, bandages, oil silk, lint, thread.
BY THE REV. SAMUEL HAUGHTON, F.R.S.,
Fellow of Trinity College, Professor of Geology in the University of Dublin, and
President of the Geological Society of Dublin.
The map which accompanies this geological description is arranged from the specimens brought home by Captain F. L. M'Clintock, R.N., from the four Arctic Expeditions in which he served from 1848 to 1859. These specimens are all deposited in the Museum of the Royal Dublin Society, and form a more extensive and better collection of Arctic rocks and fossils than is to be found in any other museum in Europe.
It will be most convenient to describe the geology of the Arctic Islands by the formations which are to be found there, which are the following:—
I shall describe these successive formations briefly, and add a few remarks of a theoretical character, to indicate the important inferences which may be drawn from the facts respecting them made known to us by M'Clintock's discoveries.
These rocks form a considerable part of North Greenland, on the east side of Baffin's Bay, and constitute the rock of the country at the east side of the island of North Devon, which forms a portion of the coast-line of the west of Baffin's Bay, and the north side of the entrance into Lancaster Sound.
1. Whale Fish Islands, lat. 69° N., are composed of a very fine-grained, flaggy, black mica schist, composed of black mica in very small plates, occasionally putting on a hornblendic lustre, and minute grains of quartz interstratified with the mica. The softer varieties are cut by the natives into grissets and cooking utensils of various shapes, some of which resemble the cambstones found in Ireland, which are made from a kind of potstone, abundant in parts of the County Donegal.
2. Upernivik, lat. 72° N., Greenland.—This district is famous for the occurrence of large quantities of plumbago, which is found in a metamorphic rock of the following character. Fine-grained, amorphous, granitoid rock, composed of minute particles of grey quartz; a honey-colored felspar of waxy lustre, of unknown composition; minute particles of red semitransparent garnet, of conchoidal fracture; and small particles, with occasional large nests, of plumbago. The plumbago occurs both amorphous, and in long acicular crystals. Sometimes the rock becomes of coarser texture and more crystalline, and the yellow color of the felspar gives place to a greenish tinge; and it sometimes also becomes a felspar of perfect cleavage, semitransparent, and white. The dodecahedral crystals of garnet reach the diameter of one inch.
The general character of the rocks near Upernivik is different from that of the rock in which the plumbago is found; they consist of a fine-grained black mica schist, with very little felspar or quartz, and intersected by thin veins of elvan composed of quartz and white felspar. The cooking utensils of the natives are made from this fine schist, in preference to any other description of rock.
3. Woman's Islands.—These islands, off the west coast of Greenland, are composed of a garnetiferous mica slate, formed of black mica in layers, with alternating plates, composed of white felspar and quartz, and filled with fine garnets, rose-colored, vitreous in fracture, and transparent.
4. Cape York, lat. 76° N., Greenland.—This cape is composed of a fine-grained granite, consisting of quartz, white felspar, with minute specks of a black mineral, of pitchy lustre, composition not yet determined.
5. Wolstenholme and Whale Sounds, lat. 77° N., Greenland.—At Wolstenholme Sound the granitoid rocks of Greenland become converted into mica slate and actinolite slate of a remarkable character. The mica slate is composed of large plates of an intimate mixture of black and white mica, the chemical examination of which will doubtless prove of interest. These plates of mica are separated by bands of pure white felspar. The actinolite slate is dark green, and formed by an almost insensible gradation from the mica slate. In the low ground between Wolstenholme and Whale Sounds, the granitic rocks cease, and are covered by deposits of fine red gritty sandstone, of a banded structure, and a remarkable coarse white conglomerate. The boundary between these formations is also marked by the development of masses of dolerite and clayey basalt.
6. Carey's Islands, 76° 40' N., Greenland, lie to the westward of Wolstenholme Sound, and are composed of a remarkable gneissose mica schist, formed of successive thin layers of quartz granules, containing scarcely any felspar, and layers of jet black mica, with occasional facets of white mica. This mica schist passes into a white gneiss, composed of quartz, white felspar, and black mica, penetrated by veins, coarsely crystallised, of the same minerals. Yellow and white sandstones are also found in small quantity on the islands, reposing upon the granitoid rocks.
7. Capes Osborn and Warrender, lat. 74° 30' N., North Devon.—The granitoid rocks between these two capes are composed of graphic granite, consisting of quartz (grey) and white felspar; this graphic granite passes into a laminated gneiss, consisting of layers of black mica and white translucent felspar, sparingly mixed with quartz: with the gneiss are interstratified beds of garnetiferous mica slate, consisting of quartz, pale greenish white felspar, black and white mica in minute spangles, and crystals of garnet, rose-colored, disseminated regularly through the mass. Quartziferous bands of epidotic hornstone occur with the foregoing beds; and the whole series is overlaid by red sandstones, of banded structure, which bear a striking resemblance to those that overlie the granitoid beds of Wolstenholme Sound.
8. North Somerset.—The granitoid rocks are found again on the west side of the island of North Somerset, where they form the eastern boundary of Peel Sound. Boulders of granite are found at a considerable distance (100 miles) to the north-eastward of the rock in situ, as at Port Leopold, Cape Rennell, etc. The general character of the granitic rocks in the north and west of North Somerset are thus described by Captain M'Clintock:—
"Near Cape Rennell we passed a very remarkable rounded boulder of gneiss or granite; it was 6 yards in circumference, and stood near the beach, and some 15 or 20 yards above it; one or two masses of rounded gneiss, although very much smaller, had arrested our attention at Port Leopold, as then we knew of no such formation nearer than Cape Warrender, 130 miles to the north-east; subsequently we found it to commence in situ at Cape Granite, nearly 100 miles to the south-west of Port Leopold.
"The granite of Cape Warrender differs considerably from that of North Somerset; the former being a graphic granite, composed of grey quartz and white felspar, the quartz predominating; while the latter, or North Somerset granite, is composed of grey quartz, red felspar, and green chloritic mica, the latter in large flakes; both the granite and gneiss of North Somerset are remarkable for their soapy feel."[30]
To the east of Cape Bunny, where the Silurian limestone ceases, and south of which the granite commences, is a remarkable valley called Transition Valley, from the junction of sandstone and limestone that takes place there. The sandstone is red, and of the same general character as that which rests upon the granitoid rocks at Cape Warrender and at Wolstenholme Sound. Owing to the mode of travelling, by sledge on the ice, round the coast, no information was obtained of the geology of the interior of the country, but it appears highly probable that the granite of North Somerset, as well as that of the other localities mentioned, is overlaid by a group of sandstones and conglomerates, on which the Upper Silurian limestones repose directly. A low, sandy beach marks the termination of the valley northwards, and on this beach were found numerous pebbles, washed from the hills of the interior, composed of quartzose sandstone, carnelian, and Silurian limestone. The accompanying sketch was made by Captain M'Clintock, on the spot, in 1849, and afterwards finished by Lieutenant Browne. It represents the island called Cape Bunny, which forms the eastern headland of the entrance of the now famous Peel Sound, down which the 'Erebus' and 'Terror' sailed, three years before it was visited by Sir James C. Ross and Lieutenant M'Clintock, in their first sledge journey on the ice. Cape Granite is the northern boundary of the granite, which retains the same character as far as Howe Harbor. It is composed of quartz, red felspar, and dark green chlorite; and is accompanied with gneiss of the same composition. I have in my possession a specimen of this granite, found as a pebble at Graham Moore Bay, Bathurst Island, S.W., a locality 135 knots distant from Cape Granite, to the N.W.
9. Bellot Strait, lat. 72° N., separate North Somerset from Boothia Felix. The 'Fox' Expedition wintered here in 1858, and had abundant means of ascertaining the geological structure of the neighborhood. The junction of the granitoid and Silurian rocks occurs in these straits, the low ground to the east being horizontal beds of Silurian limestone, while on the west the granite hills of West Somerset rise to a height of 1600 feet above the narrow straits. The granite here is of three varieties.
α. Blackish grey, fine grained, gneissose granite, composed of quartz, white felspar, and large quantities of fine grains and flakes of hornblende, passing into black mica. The gneissose beds of this granite dip 13° S.E.
β. A red granite, graphic texture, composed of quartz and red felspar, coarse grained.
γ. Syenite, composed of honey-yellow felspar and hornblende, in very large crystals, the felspar passing into red and pink, and the whole rock mass penetrated by veins of the same material, but fine grained. This variety of igneous rock was met with principally at Pemmican Rock, western inlet of Bellot Strait. Large quantities of hornblende are also met with at Levesque Harbor, Bellot Strait, composed of facetted crystals agglutinated together into large masses, forming a crystalline hornblendic gneiss.
10. Pond's Bay, Baffin's Bay, lat. 72° 40' N.—In this locality a quartziferous black mica schist underlies the Silurian limestone, and is interstratified with gneiss and garnetiferous quartz rock, all in beds, inclined 38° W.S.W. (true).
11. Montreal Island, mouth of the Fish River, lat. 67° 45' N.—The granitoid rocks, which everywhere, in the Arctic Archipelago, underlie the Silurian limestone, appear at Montreal Island as a gneiss, composed of bands of felspar (pink) and quartz (¼ inch thick), separated by thin plates composed altogether of black mica; the whole rock exhibiting the phenomena of foliation in a marked degree.
The east side of King William's Island, though composed of Silurian limestone like the rest of the island, is strewed with boulders of black and red micaceous gneiss, like that of Montreal Island, and black metamorphic clay slate, in which the crystals of mica (qu. Ottrelite) are just commencing to be developed. It is probable that the granitoid rocks appear at the surface somewhat to the eastward of this locality.
12. Prince of Wales' Island, west of Peel Sound.—The granitoid rocks extend across Peel Sound into Prince of Wales' Island, in the form of a dark syenite composed of quartz, greenish white felspar passing into yellow, and hornblende. This rock is massive and eruptive at Cape M'Clure, lat. 72° 52' N., and occasionally gneissose, as at lat. 72° 13' N. Between these two points, at lat. 72° 37' N., a limestone bluff occurs containing the characteristic Silurian fossils, and is succeeded at 72° 40' by a ferruginous limestone, bright red, and a few beds of fine red sandstone, like those observed by M'Clintock at Transition Valley, North Somerset. The entire western portion of Prince of Wales' Land is composed of Silurian limestone, which in the extreme west, at Cape Acworth, becomes chalky in character and non-fossiliferous, resembling the peculiar Silurian limestone found on the west side of Boothia Felix.
The Silurian rocks of the Arctic Archipelago rest everywhere directly on the granitoid rocks, with a remarkable red sandstone, passing into coarse grit, for their base. This sandstone is succeeded by ferruginous limestone, containing rounded particles of quartz, which rapidly pass into a fine greyish green earthy limestone, abounding in fossils, and occasionally into a chalky limestone, of a cream color, for the most part devoid of fossils. The average dip of the Silurian limestone varies from 0° to 5° N.N.W., and it forms occasionally high cliffs, and occasionally low flat plains, terraced by the action of the ice as the ground rose from beneath the sea. The general appearance of the rocks is similar to the Dudley limestone, and would strike even an observer who was not a geologist. This resemblance to the Upper Silurian beds extends to the structure of the rocks on the large scale. Alternations of hard limestone and soft shale, so characteristic of the Upper Silurian beds of England and America, arranged in horizontal layers, give to the cliffs around Port Leopold the peculiar appearance which has been described by different Polar navigators as "buttress-like," "castellated;" this appearance is produced by the unequal weathering of the cliff, which causes the hard limestone to stand out in bands. Excellent sketches of this remarkable appearance, drawn by Lieutenant Beechey, are figured at page 35 of Parry's First Voyage, 'Hecla' and 'Griper,' 1819-20. The Western side of King William's Island (now, alas! invested with so sad an interest) is a good example of the low terraced form which the limestone rocks assume at times.
The following lists contain the names of the principal fossils brought home by Captain M'Clintock:—
This is a fine slab of limestone, almost together composed of the remains of Loxonema Salteri and Atrypa phoca. It appears to have been quietly deposited at the bottom of a deep submarine depression, swarming with Pyramidellidæ and deep-water Brachiopoda. The physical conditions indicated by the fossils are also rendered probable by the rock itself, which consists of fine grey limestone, subcrystalline, and intimately blended with the finest and most delicate description of mud, such as could only be found where the water was deep, and all currents far removed.
A specimen of the same fossil coral which I have named, doubtfully, from Beechey Island, as Favosites or Calamopora Gothlandica; it is not impossible, however, that it is not a Calamopora at all, but a species of Chætetes.
Specimens of brown earthy limestone, with a fetid smell when struck with a hammer; resembles closely the limestone of Cape York, Lancaster Sound.
The limestone at this locality is white and saccharoid, with large rhombohedral crystals of calcspar.
The rock at this locality is a grey mud limestone.
The cream-colored chalky limestone found on the west side of Prince of Wales' Island here occurs, and is generally destitute of fossils, like that of Prince of Wales' Land.
The limestone here is of the same grey earthy aspect as at Beechey Island and Port Leopold.
These fossils occur in grey earthy limestone, near its junction with the red arenaceous limestone already described.
The Upper Silurian limestones already described are succeeded by a most remarkable series of close-grained white sandstones, containing numerous beds of highly bituminous coal, and but few marine fossils. In fact, the only fossil shell found in these beds, so far as I know, in any part of the Arctic Archipelago, is a species of ribbed Atrypa, which I believe to be identical with the Atrypa fallax of the carboniferous slate of Ireland. These sandstone beds are succeeded by a series of blue limestone beds, containing an abundance of the marine shells commonly found in all parts of the world where the carboniferous deposits are at all developed. The line of junction of these deposits with the Silurians on which they rest is N.E. to E.N.E. (true). Like the former they occur in low flat beds, sometimes rising into cliffs, but never reaching the elevation attained by the Silurian rocks in Lancaster Sound.
The following lists contain the principal fossils and specimens presented to the Royal Dublin Society by Captain M'Clintock and by Captain Sir Robert M'Clure.
Coal, sandstone, clay ironstone, and brown hematite, were found along a line stretching E.N.E. from Baring Island, through the south of Melville Island, Byam Martin's Island, and the whole of Bathurst Island. Carboniferous limestone, with characteristic fossils, was found along the north coast of Bathurst Island, and at Hillock Point, Melville Island.
I have marked on the map the coal-beds of the Parry Islands, which appear to be prolonged into Baring Island, as observed by Captain M'Clure. The discovery of coal in these islands is due to Parry, but the evidence of the extent and quantity in which it may be found was obtained during the expeditions of Austin and Belcher. In addition to the localities surveyed by himself, Captain M'Clintock has given me specimens of the coal found at other places by other explorers; and it is from a comparison of all these specimens that I have ventured to lay down the outcrop of the coal-beds, which agrees remarkably well with the boundary of the formations laid down from totally different data.
This interesting brachiopod was found in the limestone by Captain M'Clure, at the Princess Royal Islands, in the Prince of Wales' Strait, between Baring Island and Prince Albert Land. I have no hesitation in pronouncing it to be identical with Schlotheim's fossil, which is found in the greatest abundance at Gerolstein, in the Eifel. Banks Land, or Baring Island, is composed of sandstone, similar to that at Byam Martin's Island, and at the Bay of Mercy. This sandstone contains beds of coal, apparently the continuation of the well-known coal-beds of Melville Island. It is a remarkable fact, that these carboniferous sandstones underlie beds of undoubtedly the carboniferous limestone type, and that at Byam Martin's Island, where fossils are found in this sandstone, they are allied to Atrypa fallax and other forms characteristic of the lower sandstones of the carboniferous epoch. It is, therefore, highly probable that the coal-beds of Melville Island are very low down in the series, and do not correspond in geological position with the coal-beds of Europe, which rest on the summit of the carboniferous beds. It is interesting to find at Princess Royal Island, where, from the general strike of the beds, we should expect to find the Silurian limestone underlying the coal-bearing sandstones, that this limestone does occur, and contains a fossil, T. aspera, eminently characteristic of the Eifelian beds of Germany, which form, in that country, the Upper Silurian Strata.
Fine specimens of coal.
Sandstone passing into blue quartzite.
Fine yellow and grey sandstone.
Bituminous coal, with finely divided laminæ, associated with brown crystalline limestone, with cherty beds, and grey-yellowish sandstone, passing into brownish-red sandstone.
Nodules of clay ironstone, very pure and heavy, associated with ferruginous fine sandstone and coal of the usual description.
The hill-tops and sides along the south shore of Liddon's Gulf, and as far as Cape Dundas, are generally bare, composed of frozen mud, arising from the disintegration of shale, the annual dissolving snows washing them down and giving them a rounded form. The southern slopes generally support vegetation. Fragments of coal are very frequently met with, and at the mouth of a ravine on the south shore of Liddon's Gulf there is abundance, of very good quality; it contains a considerable quantity of pyrites or bisulphuret of iron.
The sandstone of Byam Martin's Island is of two kinds—one red, finely stratified, passing into purple slate, and very like the red sandstone of Cape Bunny, North Somerset, and some varieties of the red sandstone and slate found between Wolstenholme Sound and Whale Sound, West Greenland, lat. 77° N. The other sandstone of Byam Martin's Island is fine, pale-greenish, or rather greyish-yellow, and not distinguishable in hand specimens from the sandstone of Cape Hamilton, Baring Island. It contains numerous shells and casts of a terebratuliform brachiopod, closely allied to the Terebratula primipilaris of Von Buch, found abundantly at Gerolstein in the Eifel. On the whole, I incline to the opinion that the sandstones, limestone, and coal of Byam Martin's Island, are the corresponding rocks of Melville Island, Baring Island, and Bathurst Island, are low down in the Carboniferous System, and that there is in these northern coal-fields no subdivision into red sandstone, limestone, and coal-measures, such as prevails in the west of Europe. If the different points where coal was found be laid down on a map, we have in order, proceeding from the south-west—Cape Hamilton, Baring Island; Cape Dundas, Melville Island, south; Bridport Inlet and Skene Bay, Melville Island; Schomberg Point, Graham Moore Bay, Bathurst Island; a line joining all these points is the outcrop of the coal-beds of the south of Melville Island, and runs E.N.E. At all the localities above mentioned, and, indeed, in every place where coal was found, it was accompanied by the greyish-yellow and yellow sandstone already described, and by nodules of clay ironstone, passing into brown hematite, sometimes nodular and sometimes pisolitic in structure.
Coal of the usual quality.
At Cape Lady Franklin, and at many other localities along the north shore of Bathurst Island, carboniferous fossils in limestone, clay ironstone balls passing into brown hematite, cherty limestone, and earthy fossiliferous limestone, with the same species of Atrypa as at Byam Martin's Island, were found in abundance by Sherard Osborn, Esq., Commander of H.M.S. 'Pioneer,' in whose journal the following note respecting them may be found:—
"The above collection was delivered over to Captain Sir Edward Belcher, C.B., by Commander Richards, at 2 P.M., on 7th Nov. 1853."[35]
It is to be hoped that they may soon be made available for the elucidation of the geology of this most interesting portion of the Arctic discoveries.
In this locality abundance of vesicular scoriaceous trap rocks were found by Captain M'Clintock; they appear to me to be the representatives of the volcanic rocks found everywhere at the commencement of the carboniferous period.
The Syringopore found at Cornwallis Island appears to be identical with the variety of the Irish carboniferous S. geniculata, in which the corallites are at a distance from each other somewhat exceeding their diameters, and in which the connecting tubes are about two diameters apart.
A question of very considerable geological interest is raised by the occurrence together of corals, in the same locality, of silurian and carboniferous forms.
I entertain no doubt of their being in situ, and occurring in the same beds, for the following reasons:—
1st. The Syringopores of Griffith's Island were found at an elevation of 400 feet above the sea, and, therefore, could not be brought by drifting ice.
2nd. The specimens were apparently of the same texture and composition as the native rock, whenever the latter was visible from under the snow.
3rd. I do not believe in the lapse of a long interval of time between the silurian and carboniferous deposits,—in fact, in a Devonian period.
4th. The same blending of corals has been found in Ireland, the Bas Boulonnais, and in Devonshire, where silurian and carboniferous forms are of common occurrence in the same localities.
5th. In the carboniferous beds proper of Melville Island and Bathurst Island, there were not found, so far as I am aware, any corals of the same character as those at Griffith's Island, Cornwallis Island, and Beechey Island, which could give a supply to be drifted to the latter localities in a Pleistocene sea. It is plain, from the height at which the corals were found that, if they were brought to their present localities by ice, it must have been during the period known as Post-tertiary, as the present conditions of drift-ice in Barrow's Straits do not permit us to suppose them to have been placed where we now find them by existing causes.
The occurrence of coal-beds in such high latitudes has been speculated on by many geologists—in my opinion, not very satisfactorily; as it is very difficult to conceive how, even if the question of temperature was settled, plants even of the fern and lycopodium type could exist during the darkness of the long winter's night at Melville Island. This difficulty is increased by the facts made known to us by the discovery of ammonites and lias fossils in Prince Patrick's Island by Captain M'Clintock.
Many years ago it was asserted by Lieutenant Anjou, of the Russian navy, that ammonites had been found by him in the cliffs on the south shore of the island of New Siberia, off the north coast of Asia, in lat. 74° N. This statement, which was published in Admiral Von Wrangel's journal, attracted but little attention, until it was confirmed, as far as probability of such fossils occurring at so high a latitude is concerned, by the remarkable discovery of similar fossils by Captain M'Clintock, in lat. 76° 20' N., at Point Wilkie, in Prince Patrick's Island.
In a paper, published by the Royal Dublin Society, in the first volume of their journal, p. 223, Captain M'Clintock thus describes the finding of these fossils:—
"After returning to Cape de Bray, we took up the provisions that the officer after whom it is called had left for us, and crossed the strait to Point Wilkie; reached it on the 14th May. This traverse was the more difficult from the great load upon our sledge, and the unfavorable state of the ice and snow. The freshly fallen snow was soft and deep, and beneath it the older snow lay in furrows across our route, hardened and polished by the winter gales and drifts, so that it resembled marble.
"On landing I found the beach low, composed of mud, with the foot-prints of animals frozen in it. A few hundred yards from the beach there are steep hills, about 150 feet in height, and upon the sides of these, in reddish-colored limestone, casts of fossil shells abound. Inland of these, the ordinary pale carboniferous sandstone and cherty limestone re-appeared. The fossils are all small, and of only a few varieties, some being ammonites, but the greater part bivalves. They differed from any I had met with before, and the rock was almost brick-red; I picked up what appeared to be fossil bone (Ichthyosaurus?), only part of it appearing out of the fragment of the rock.
"Point Wilkie appears to be an isolated patch of liassic age, resting upon carboniferous sandstones and limestones, with bands of chert, of the same age as the limestones and sandstones of Melville Island. The eastern shores of Intrepid Inlet is composed of this formation; while the western, rising into hills and terraces, is of the underlying carboniferous epoch. At the western side of Intrepid Inlet I found upon the ice a considerable quantity of white asbestos, but did not ascertain from whence it had been brought."
The fossils thus found in situ, I have no doubt, belong to the liassic period; and as their geological interest is indubitable, I offer no apology for inserting here the following description, written by me on Captain M'Clintock's return to Dublin from his third Arctic expedition.
LIAS FOSSILS.
(a) Ammonites M'Clintocki (Haughton).—Testâ compressâ, carinatâ, anfractibus latis, lateribus, complanatis, transversim undato-costatis; costis simplicibus, juxtâ marginem interiorem levigatis; dorso carinato acuto; aperturâ sagittatâ, compressâ, antice carinatâ; septis lateribus 4-lobatis.
This fine ammonite resembles several species common in the upper lias of the Plateau de Larzac, Sevennes, in France. It approaches A. concavus of the lower Oolite, but is distinguished by having only four lobes on the lateral margins of the septa, and by its showing no tendency to a tricarinated keel. The following measurements give an exact idea of its form, as compared with that of the species mentioned:—