In general terms it may be stated that all the species of Foraminifera found in the Post-pliocene stiil inhabit the Gulf and River St. Lawrence. Several species found in the Gulf of St. Lawrence have not yet been recognized in the Post-pliocene, and these are mostly inhabitants of depths exceeding 90 fathoms, or among the more southern forms found in the Gulf.

On the whole, the assemblage, as in the northern part of the Gulf of St. Lawrence at present, is essentially arctic, and not indicative of very great depths.

The sandy forms which are not uncommon in the Gulf are very rare in the Post-pliocene; but this may be accounted for by the greater difficulty of washing them out of the clay, or possibly their cementing material may have decomposed, allowing them to fall to pieces. As the epidermal matter of shells is often preserved, the last supposition seems less likely. The Leda clays are, however usually very fine and calcareous, so that there was probably more material for calcareous than for arenaceous forms.

The Foraminifera are very generally diffused in the Post-pliocene clays, though much more abundant in some layers than in others. They may easily be detected by a pocket lens, and are usually in as fine preservation as recent specimens, especially in the deeper and more tenacious layers of the Leda clay. They are however, usually most abundant in the somewhat arenaceous layers near the top of the Leda clay, and immediately below the Saxicava sand, and especially where this layer contains abundance of shells of Mollusca. I have nowhere found them more abundant or in greater variety than at the Glen Brick-work, Montreal, on the McGill College Grounds, and at Logan's Farm. At the Glen Brick-work a few worn specimens of Polystomella are contained in the beds underlying the Leda clay and equivalent to the Boulder-clay, which, however, has in general, in the vicinity of Montreal as yet afforded no marine fossils.

In searching for Foraminifera in the clays of Rivière-du-Loup, I have observed in the finer washings several species of Diatomace; among these a species of Coscinodiscus very frequent in the deeper parts of the Gulf of St. Lawrence. But on the whole Diatoms appear to be rare in these deposits. In the Rivière-duLoup clays I have also observed the pollen grains of firs and

spruces.

The nomenclature used above is that of Parker and Jones, in their paper on the North Atlantic Soundings, in the Transactions

VOL VI.

I

No. 3.

of the Royal Society. For figures of the species, I may refer to that memoir, and to my previous papers published in the Naturalist.

Tethea Logani, Dawson.

(2) Porifera.

Leda clay, Montreal. This species has not yet been recognised in a living state, though allied to Tethea hispida, Bowerbank, of the coast of Maine. Its spicules in considerable masses, looking like white fibres, are not uncommon in the Post-pliocene at Montreal.

Tethea?

Another silicious sponge is indicated by little groups of small spicules found at the Tanneries, near Montreal, by Mr. G. T. Kennedy, and at Riviere-du-Loup by the author. Its spicules are long and acerate, and much more slender than those of Tethea Logani. They resemble those of T. hispida, recent on the coast of Maine, and also those of a species of Polymastia, dredged by Mr. Whitcaves in the Gulf of St. Lawrence.

CLASS II-ANTHOZOA.

CLASS III-HYDROZOA.

No distinct organisms referable to the above groups have yet been found in the Post-pliccene deposits of Canada. As our recent fauna includes no stony coral, and the recent species of the Gulf of St. Lawrence have no parts likely to be preserved other than minute spicules, this is not to be wondered at. In washing the clays for Foraminifera, however, numerous fragments are obtained, which resemble portions of the horny skeletons of hydroids, though not in a state admitting of determination.

CLASS IV. ECHINODERMATA.

(1) Ophiuridea.

Ophioglypha Sarsii, Lutken.

Fossil-Leda clay, near St. John, N. Brunswick; Mr. Matthew. Recent River St. Lawrence, at Murray Bay; also found of large size in deep water in the Gulf of St. Lawrence, by Mr. Whiteaves.

Ophiocoma.

Fragments of a small species of ophiuroid starfish not determinable, have been found in the Leda clay at Montreal, and in nodules at Green's creek.

(2) Echinoidea.

Euryechinus drobachiensis, Müller.

Fossil-Leda clay, Beauport; Rivière-du-Loup; Montreal. This species is rare in the Post-pliocene, but very common in all parts of the Gulf of St. Lawrence at present.

(3) Holothuridea.

Psolus phantopus? Oken.

Scales of an animal of this kind have been found in the Leda clay at Montreal. They may belong to P. phantopus, or to the species P. (Lophothuria) Fabricii, also found on our coasts.

ON THE ORIGIN AND CLASSIFICATION OF
ORIGINAL OR CRYSTALLINE ROCKS.
By THOMAS MACFARLANE.

(Continued from page 312-Vol. V.)

V. MINERALOGICAL CONSTITUTION.

Having, in the foregoing, adverted to the texture and chemical composition of original rocks, it now becomes necessary to refer more particularly to their mineralogical constitution. In order to continue the analogy which has been shewn to exist between furnace slags and original rocks, it will be well here to refer to those instances which have been observed of the formation of well developed crystals in the cooling of artificial silicates. The rapid manner in which furnace slags are commonly allowed to cool is of course detrimental to the formation of any mineral-like aggrega. tions, but it is sometimes possible to observe in copper furnace slags that, when they have been allowed to solidify in large blocks or cakes, they shew an actynolitic structure in their mass, often. closely resemble hornblende rock, and very commonly contain cavities lined with the most beautiful crystals. The formation of pyroxene in slags from iron furnaces has been frequently observed

and well authenticated. Nöggerath described augite crystals from the slags of the iron furnace of Olsberg near Bigge in Westphalia. Montefiori Levi analysed augites taken from the slags of the iron furnace at Augreé near Liege. Richter described and examined similar crystals from the iron works of Rufskberg in the Banat; Von Leonhard mentions acicular augite crystals in the iron furnace slags of Skis-hytta in Sweden. F. Sandberger describes similar occurences; and numerous others might here be mentioned. Mitscherlich and Berthier obtained by melting silica, lime, and magnesia together, in a charcoal crucible placed in a porcelain furnace, a mass possessing cleavage corresponding to the faces of augite, and the hollow cavities in which were crowded with the most beautiful crystals of that mineral. These are also of very common occurrence in the lava streams not only of extinct but of active volcanoes; and well-developed augite crystals have not unfrequently been ejected from their craters. Olivine has been. observed in the slags of iron furnaces quite as frequently as augite, and it, as well as magnetite, is one of the commonest minerals in streams of basaltic lava. So is leucite, although it has not yet been produced artificially. Mitscherlich observed transparent six-sided tabular crystals of mica, and leaves of it several inches broad, in the cavities of old copper furnace slags near Garpenberg in Dalecarlia. Gurlt also mentions artificially formed mica, and it ap pears frequently in ancient and modern lava streams. With regard to felspar, Hausmann makes mention as early as 1810, of felspar crystals which had been formed in one of the Mansfield. furnaces. In 1834 Herne found similar crystals in the copper furnace of Sangershausen after it had been blown out, and in the iron furnace of Josephshütte in the Hartz, they were also detected. In 1810 the formation of felspar crystals in glass works was first observed; and in 1848 Prechtl gave an account of their occurring in a mass of glass weighing 1333 lbs. which had been melted. in the plate glass factory at Neuhaus. They were of various sizes, some an inch in length, with perfectly sharp edges. The formation of sanidine and other varieties of felspar, in lavas of recent age, is a matter of common occurrence. No instance is known of the production of quartz from artificial silicates, nor do those lavas of the present day which are highly siliceous, develope it.in cooling. These solidify as vitreous uncrystalline masses, but many lavas of extinct volcanoes in the Andes and the Siebengebirge contain it in well-formed crystals, shewing that it must have crystallized out from the mass of the rock.

The number of minerals which enter into the constitution of rocks is very small compared with the number of the mineral species which are found described in the various treatises on mineralogy. Of the latter there are upwards of six hundred, but the great majority of these are rare minerals, occurring in veins or cavities, and not entering into the constitution of the rocks themselves. The number of minerals which are found in original rocks is still more limited, and if from it if we deduct the sparingly occurring, or so-called accessorial constituents. the number is reduced to twenty minerals, which may be called the essential constituents of original rocks. The following table gives their names and the silica contents of the extreme acid and basic varieties.

The separation of the minerals occurring in rocks into essential and accessorial constituents originated with German lithologists and may perhaps be regarded as arbitrary. In characterising the sixteen minerals just mentioned as essential constituents, we have however, to some extent, been guided by their chemical constitution. In the preceding chapter silicic acid, alumina, peroxide of iron, protoxide of iron, magnesia, lime, soda and potash were indicated as the essential chemical constituents of rocks; and only such minerals as contain these substances, and no others, as essential ingredients, have been admitted into the table. This mode of selection may perhaps be considered as arbitrary as any other, for it causes the exclusion of the mineral tourmaline, which sometimes appears to deserve the rank of an essential constituent.