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like the overlying dark limestones, is not used for the more important building purposes, must have been, when recent, a chalky Tock, made up of very minute fragments of shells and corals; but it has been blackenerl by the carbonization of its organie matter, and hardened by the penetration of a caleareous cement; still its general structure under the microscope is not dissimilar from that of chalk. It contains multitudes of nsinute unbroken shells, some of which have much the aspect of foraminifera, as may be seen in Fig. 1; but they may possibly be univalve mollusks. I

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Fig. 1.- Earthy Trenton Limestone, Montreal, (20 diams.) hope, however, by the examination of a larger number of speci. mens, to determine whether minute foraminifera really occur in these ancient beds.

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Fig. 2.-Crystalline Trenton Limestone, Montreal, horizontal section,

(10 diameters.) In the coarse grained variety the materials are somewhat loosely placed, and in a horizontal section like Fig. 2, may appear quite

disconnected, but in a vertical section they are seen to rest upon one another, and sometimes to be very closely packed, as in Fig. 3, in which translucent fragments of crinoids are seen to be

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Fig. 3.—Trenton Limestone, Montreal, vertical section, (10 drams.) packed in broken corals, chiefly Ptilodictya, and the irregularity of the planes of deposition is marked by two slender bands of fine black earthy and organic slime.

The beds of this remarkable organic limesione are usually very uneven on the surface—the smaller beds very much so; and on these surfaces there often appear quantities of Monticulipora and Ptilodictya in a perfect state, as well as occasionally Brachiopoda, Ortboceratites and Trilobites. Between the beds occurs a black shaly material consisting principally of clay and fine sand, darkened by carbonaceous matter, and containing more or less of fragments of shells and corals. The beds of organic fragments now constituting the gray limestone, must have been drifted over the bottom by strong and apparently somewhat irregular currents, in which in every favorable spot corals fixed themselves and grew. The black shale appears to have settled in the form of fine mud, which often coats over, as with a varnish, the surfaces of the limestone and the fossils lying on them; and which has usually only partially filled up the depressions of the surface, previous to the deposition of a new bed of the grey limestone. In the upper part of the Trenton formation at Montreal, the earthy matter so far prevails that the limestone becomes black and compact, and is interstratified with much shale, but it still contains numerous organic fragments, which in some beds become predominant.

The Trenton and its associated limestones are widely distributed rocks. Their outcrop runs from Quebec along the north shore of the St. Lawrence to Montreal—then southward through the valley of Lake Champlain into New York, where it skirts the Azoic region of the Adirondack, and returning northward along the valley of the Black river, re-enters Canada at the lower end of Lake Ontario, along which these limestones extend in a broad band, and crossing to Lake Huron stretch along the chain of the Manitoulin Islands, and then run again to the southwari along the west side of Lake Michigan. There are also in Canada outlying patches on the Ottawa and Lake St. John. Throughout all these regions the gray crystalline beds are more or less represented ; though in the State of New York they appear to be in the upper part of the formation, and to thin out and disappear toward the South.* Specimens from Chateau Richer below Quebec, from Ottawa, from the La Cloche mountains, and from great Manitoulin Island, exhibit very nearly the same microscopic characters with those of the Montreal quarries. In the stone of Chateau Richer crinoids predominate. In that of Ottawa there is a greater prevalence of fragments of shells. In that of La Cloche and Manitoulin the materials are much the same as at Montreal.

The conditions of the accumulation of this great and extended mass of animal fragments, it is not difficult to understand. An ocean area, probably not of great depth, the growth of multitudes of branching corals and crinoids, the destruction of these by the waves and by the death of successive generations, the drifting of their remains by currents over the bottom, the occasional invasion of the clear water by muddy sediment—these are the conditions which must have prevailed when the gray Trenton limestones were formed. Professor Hall and Mr. Billings have remarked that the Brachiopod shell-fish of the Chazy and Trenton are usually of smaller size than that which they attain in overlying formations. This may have been due to the conditions so favorable to the spreading of organic fragments over the sea bottom.

In the Island of Montreal the Black river and Chazy limestones crop out from beneath the Trenton. The quarries at Pointe Claire, worked for the Victoria Bridge, are believed by Sir W. E. Logan to represent principally the former. The western or back quarries on the Mile End road and those of Isle Jesus belong to the latter. The stone worked for the piers of the Victoria Bridge presents several varieties in alternate layers. One of these has the coarse crystalline aspect of the gray Trenton, but it consists principally of fragments of Brachiopodous shells; masses of coral however occurring in some layers. A finer variety which constitutes a large proportion of the stone, is made up of rounded and comminuted

• See Geological Surveys of Canada and New York.

fragments of shells and crinoids, which, like the fragments of some of the modern limestones of Florida, bear evidence of the rolling action of the surf or of strong currents. Another variety is fine and compact like the upper part of the Trenton at Montreal, and shows a homogeneous calcareous and earthy paste filled with fragments of shells, crinoids, and corals. Figs. 4 and 5 represent the

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Fig. 5. Figs. 4 & 5.---Limestone from Pt. Claire Quarries, (10 diams.) two last varieties, and may be taken as fair specimens of the material of the piers of the great railway bridge, which solid and durable though they are, are composed of shelly fragments, that once drifted like snow before the ocean currents. The Chazy limestone of Isle Jesus is characterised by Sir W. E. Logan, as "a cemented aggregation of organic remains.” I have not examined this stone, but that of the same formation in the vicinity of Montreal, consists almost entirely of broken brachiopodous shells, many of them probably the Atrypa plena, which is so abundant in these same beds. (Fig. 6.)

To persons unfamiliar with such subjects, it is a striking fact that the buildings of our cities are constructed of the debris of the skeletons of marine animals, belonging to a bygone period of the earth's history, and that these same remains constitute sheets of limestone extending over many thousands of square miles, with a thickness of several hundred feet. As already stated, however, these facts are very familiar to Geologists ; yet they merit, especially with regard to the older formations, more attention in some res

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Fig. 6.-Chazy Limestone, Island of Montreal, (10 diams.) pects than they have hitherto received. Microscopic examinations of organic limestones may serve to show the precise species which have most contributed to their accumulation, and the conditions under which their remains were spread abroad, and cemented into stone. They might also serve to identify limestones not containing entire organic remains, by showing the species out of whose fragments they had been formed. To do anything really valuable toward these objects, would require the patient preparation and examination of a great number of specimens; but, to any one who has leisure for the task, it might form a very interesting field of study.

ARTICLE XII.— On Ozone. By CHARLES SMALLWOOD, M.D.,

LL.D., Professor of Meteorology in the University of
McGill College, Montreal.

(Presented to the Natural History Society.) The investigations on the nature and properties of Ozone, have within the few past years engaged the attention, and become the subject of enquiry, alike of the chemist, the meteorologist and the physician. The chemist has found its manifestations and properties approximate to, if not identical with Oxygen in a peculiar state of existence or development. The meteorologist (especially of the European continent) has proclaimed it to be the instrument, or medium, that Provider.ce has secured to provide for the production of the grand phenomena of nature ; that its action can explain the formation of all meteors, as well as the fluctuation and diurnal changes in the pressure of the atmosphere indicated by the oscillations of the Barometer, and that it is the true cause and

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