mound. This same effect upon frozen earth had caused in some places during the past winter the cracking of the ground with loud reports, which had alarmed people in the vicinity."

Some discussion ensued as to the hollowness of the crystal which did not seem satisfactorily accounted for. It was suggested, however, that the enclosed water must have found means of escape ere the solidification was complete.

We close our brief and imperfect notice of the Physical section. with two papers by Prof. Smallwood. One of these related to that mysterious substance, or probably modification of the oxygen of the atmosphere, OZONE. The other was an interesting account of the METEOROLOGY OF MONTREAL AND ITS VICINITY These papers we do not at present notice more at length, as we hope to have the papers themselves for publication.

SECTION OF NATURAL HISTORY AND GEOLOGY.

The first paper in this section, by Mr. Snell, described some processes for the quantitative assay of chromium by the blowpipe. The next was that on Sternbergia, by Prof. Dawson, which we publish in the present number. Mr. Lesley then read a description of some curious Flexures of the strata, in the Broad-top coal field of Pennsylvania, which he attributed to enormous lateral pressure acting on soft beds, compressed between sheets of inflexible sandstone. The results, as exhibited by Mr. Lesley, from actual measurements, are very singular, and most perplexing to the miner and geological observer.

Sir W. E. Logan then read a paper explanatory of the destinction between the great series of ancient metamorphic rocks which he had named respectively the

HURONIAN AND LAURENTIAN SERIES OF CANADA.

"The sub-silurian azoic rocks of Canada occupy an area of nearly a-quarter of a million of square miles. Independent of their stratification, the parallelism that can be shown to exist between their lithological character and that of metamorphic rocks of a later age, leaves no doubt in my mind that they are a series of very ancient sedimentary deposits in an altered condition. The further they are investigated, the greater is the evidence that they must be of very great thickness, and the more strongly is the conviction forced upon me that they are capable of division into

stratigraphical groups, the superposition of which will be ultimately demonstrated; while the volume each will be found to possess, and the importance of the economic materials by which some of them will be characterised, will render it proper and convenient that they should be recognized by distinct names, and represented by different colors on the geological map. So early as the year 1845, as will be found by my report on the Ottawa district (presented to the Canadian Government the subsequent year), a division was drawn between that portion which consists of gneiss and its subordinate masses, and that portion consisting of gneiss interstratified with important bands of crystalline limestone. I was disposed to place the lime-bearing series above the uncalcareous, and although no reason has since been found to contradict this arrangement, nothing has been discovered especially to confirm it: while the complication which subsequent experience has shewn to exist in the folds of the whole, (apparent dips being from frequent overturns, of little value,) would induce me to suspend any very positive assertion in respect to their relative super-position, until more extended examination has furnished better evidence. In the same report is mentioned among the azoic rocks, a formation occurring on Lake Temiscaming, and consisting of silicious slates and slate comglomerates, overlaid by pale sca-green and slightly greenish-white sandstone with quartzose conglomerates. The slate conglomerates are described as holding pebbles and boulders (sometimes one foot in diameter,) derived from the subjacent gneiss, the boulders displaying red feldspar, translucent quartz, green hornblende and black mica, arranged in parallel layers, which present deflections, according with the attitude in which the boulders were accidentally enclosed. From this it is evident that the slate conglomerate was not deposited until the subjacent formation had been converted into gneiss, and very probably greatly disturbed, for while the dip of the gneiss, up to the immediate vicinity of the slate conglomerate, was usually at high angles, that of the latter did not exceed nine degrees, and the sandstone above it was nearly horizontal. In the report transmitted to the Canadian Government in 1848, on the North Shore of Lake Huron, similar rocks are described as constituting the group which is rendered of such economic importance from its association with copper lodes. This group consists of the same silicious slate and slate conglomerate, holding pebbles of syenite instead of gneiss, similar sandstones, some of them tinged green, and similar quart

zose conglomerates, in which blood-red jasper pebbles become largely mingled with those of white quartz, and in great mountain masses predominate over them. But the series is here much intersected and interstratified with greenstone trap, which was not observed on lake Temiscaming.

These rocks were traced along the north shore of Lake Huron, from the vicinity of Sault Ste. Marie for 120 miles, and Mr. Murray ascertained that their limit on the Lake Shore occurred near Shibahahnahning, where they were succeeded by the underlying group. The position in which the group was met with on Lake Temiscaming is 130 miles to the north east of Shibahahnahning, and last year Mr. Murray, in exploring the White Fish River, was enabled to trace the out-crop of the group characterized by slates, sandstones, conglomerates, greenstones, and copper-lodes for sixty five miles from Shibahahnahning to the junction of the Maskinongé and Sturgeon rivers, tributary to Lake Nipissing. The general bearing of the out-crop is N. E., and an equal additional distance in the same direction, would strike the exposure on Lake Temiscaming. In the portion which Mr. Murray examined last year, the dip appears to be about N. W., often at a high angle, while that of the subjacent gneiss is more generally S. E., sometimes at a low angle, and in some places nearly horizontal. To the eastward of this out-crop, Canada has an area of 200,000 square miles; this has yet been but imperfectly examined, but in so far as investigation has proceeded, no similar series of rocks has been met with in it; and it may safely be asserted that none exists between the basset of the Lower Silurian and the gneiss, from Shibahahnahning to the Mingan Islands, a distance of more than 1,000 miles, and probably still farther to Labrador. The group on Lake Huron we have computed to be about 10,000 feet thick, and from its volume, its distinct lithological character, its clearly marked date, posterior to the gneiss, and its economic importance as a copper-bearing formation, it appears to me to require a distinct appellation and a separate color on the map; without which, indeed, the investigation of Canadian geology could not be conveniently carried on. We have in consequence given to the series the title of Huronian. A distinctive name being given to this portion of the Azoic rocks renders it necessary to apply one to the remaining portion. The only local one that would be appropriate in Canada, is that derived from the Laurentide range of mountains, which is composed of it from Lake Huron to Labrador. We have therefore, designated it

C

as the Laurentian series. These local names are, of course, only provisional, devised for the purpose of avoiding periphrastic or descriptive titles, the use of which has been found inconvenient; and they can be changed when more important developements, proved to be the equivalents of the series, are met with elsewhere.

In answer to a question whether these Huronian Rocks were older than the Silurian, or whether there was any indication of their being Silurian metamorphosed; Sir William said the Huronian rocks lie unconformably under the Silurian, and that the lower beds of the Silurian in contact with the Huronian are made up of its ruins. They found the Huronian in nearly a vertical attitude, but there is no possibility of doubt as to the comparative age of the Huronian and Silurian rocks."

ORIGIN OF MAGNESIAN ROCKS.

Mr. T. Sterry Hunt then read a very interesting paper on Mineral Waters and on the origin of Magnesian Rocks. "He alluded first to the deposits of mineral springs and especially of calcareous waters, as having played an important part in the formation of rocks. The deposits of such waters are however generally destitute of carbonate of magnesia, which is held in solution by them, and only precipitated on evaporation. Carbonate of soda is very abundantly distributed in certain mineral waters, and these mingling with sea-water, or with mineral waters analogous to it in their nature, have at first the effect of eliminating the lime as a carbonate, leaving the greater part of the magnesia in solution, ready to be precipitated in part by evaporation, or more completely by the farther addition of carbonate of soda. In this way dolomites may be deposited in the open sea, and may form, as they often do, the cementing material of conglomerate or coralline limestones. They may be equally formed by the evaporation in limited basins or lagoons, of waters holding carbonate of magnesia dissolved in the manner above described; in the latter case, we can easily understand the precipitation of magnesian carbonate unmixed with lime. The interstratification of dolomites with pure limestones in the Silurian rocks of Canada, was described as irreconcilable with the hitherto received theories of the origin of dolomites, and it was maintained that the hypothesis now proposed, is the only one which meets the conditions of the problem."

SUBSIDENCE OF LANDS.

Professor G. H. Cook, of Rutger's College, then read a paper on the subsidence of the land on the sea coast of New Jersey and

the adjoining States. "Mr. Cook said that in the course of some geological examinations near the coast of Southern New Jersey, his attention was frequently called to various facts indicating a change in the relative level of the land and water at some recent period. An attentive examination of these facts led him to the conclusion that a gradual subsidence of the land was now in progress throughout the whole length of New Jersey and of Long Island; and from information derived from others, he was induced to think that this subsidence might extend along a considerable portion of the Atlantic coast of the United States. The occur. rence of timber in the marshes and water below tide-level was common along their whole Atlantic shore. Almost every one familiar with shore-life had observed the remains of logs, stumps, and roots in such places, although they had been looked upon generally as the remains of trees torn from their original place of growth by torrents, or by the necessary moving of the shores, and deposited in the places where they were found by the ordinary action of the water. But close examination made it evident that they grew upon the spots where they are found. The stumps remain upright-their roots are still fast in the firm loamy ground which underlies the marsh, and their bark and small roots remain attached to them. The localities in which they are most abundant are such as are least liable to be affected by the violent action of the water or of storms. Thus they are by far the most abundant on the low and gently sloping shores of Long Island, New Jersey, and all the States farther South which are protected from the violent action of the surf by a line of sand beaches, at the same time that the numerous inlets allow free access to the tides. In these protected situations hundreds and even thousands of acres can be found in which the bottom of the marshes and bays is as thickly set with the stumps of trees as is the ground of any living forest. His own observations were chiefly made upon the southern part of New Jersey, following the shores of Delaware Bay from its head down to Cape May, and the Atlantic shore from Cape May north to Great Egg Harbor, and thence eastward at several points along the south shore of Long Island. In the ditches in the marshes, above Salem, great numbers of the stumps and trunks of trees are met with at all depths, quite down to the solid ground. At Elsinboro' Point, a little farther down on the Delaware Bay shore, the cutting away of the marsh by the water has left great numbers of stumps exposed, where they can be seen at every low