sweeps it, with the similar material of many other Alpine streams, into the Mediterranean, to aid in filling up the bottom of that sea, whose blue waters it discolours for miles from the shore, and to increase its own ever enlarging delta which encroaches on the sea at the rate of about half a mile per century. The upper waters of the Rhone, laden with similar material, are filling up the Lake of Geneva; and the great deposit of 'loess' in the alluvial plain of the Rhine, about which Gaul and German have contended since the dawn of European history, is of similar origin. The mass of material which has thus been carried off from the Alps, would suffice to build up a great mountain chain. Thus by the action of ice and water "The mountain falling cometh to naught And the rock is removed out of its place." Many observers who have commented on these facts have taken it for granted that the mud thus sent off from glaciers, and which is so much greater in amount than the matter remaining in their moraines, must be ground from the bottom of the glacier valleys, and hence have attributed to these glaciers great power of cutting out and deepening their valleys. But this is evidently an error, just as it would be an error to suppose the flour of a grist-mill ground out of the mill-stones. Glaciers it is true groove and striate and polish the rocks over which they move, and especially those of projecting points and slight elevations in their beds, but the material which they grind up is principally derived from the exposed frost-bitten rocks above them, and the rocky floor under the glacier is merely the nether mill-stone against which these loose stones are crushed. The glaciers in short can scarcely be regarded as cutting agents at all, in so far as the sides and bottoms of their beds are concerned, and in the valleys which the old glaciers have abandoned, it is evident that the torrents which have succeeded them have far greater cutting power." "In conclusion, I would wish it to be distinctly understood, that I do not doubt that at the time of the greatest post-pliocene submergence of Eastern America, at which time I believe the greater part of the boulder clay was formed, and the more important striation effected, the higher hills then standing as islands would be capped with perpetual snow, and through a great part of the year surrounded with heavy field and barrier ice, and that in these hills there might be glaciers of greater or less extent. Further it should be understood that I regard the boulder clays of the St. Lawrence valley as of different ages, ranging from the early post-pliocene to that at present forming in the gulf of St. Lawrence. Further, that this boulder clay shows in every place where I have been able to examine it, evidence of sub-aquatic accumulation, in the presence of marine shells or in the unweathered state of the rocks and minerals enclosed in it, conditions which, in my view, preclude any reference of it to glacier action, except possibly in some cases to that of glaciers stretching from the land over the margin of the sea, and forming under water a deposit equivalent in character to the 'boue glaciare' of the bottom of the Swiss glaciers. But such a deposit must have been local, and would not be easily distinguishable from the marine boulder clay. I have not had opportunities to study the boulder clay of Scotland, which in character and relations so closely resembles that of Canada, but I confess several of the facts stated by Scottish Geologists lead me to infer that much of what they regard as of sub-aerial origin must really be marine, though whether deposited by ice-bergs or by the fronts of glaciers terminating in the sea, I do not pretend to determine. It must however be observed that the antecedent probability of a glaciated condition is much greater in the case of Scotland than in that of Canada, from the high northern latitude of the former, its more hilly character, and the circumstance that its present exemption from glaciers is due to what may be termed exceptional and accidental geographical conditions; more especially to the distribution of the waters of the Gulf stream, which might be changed by a comparatively small subsidence in Central America. To assume the former existence of glaciers in a country in north latitude 56°, and with its highest hills, under the present exceptionally favourable conditions, snow-capped during most of the year, is a very different thing from assuming a covering of continental ice over wide plains more than ten degrees farther south, and in which, even under very unfavourable geo. graphical accidents, no snow can endure the summer sun, even in mountains several thousand feet high. Were the plains of North America submerged and invaded by the cold Arctic currents, the Gulf stream being at the same time turned into the Pacific, the temperature of the remaining North American land would be greatly diminished; but under these circumstances the climate of Scotland would necessarily be reduced to the same condition with that of South Greenland or Northern Labrador. As we know such a submergence of the land to have occurred in the Post-pliocene period, it does not seem necessary to have recourse to any other cause for either side of the Atlantic. It would, however, be a very interesting point to determine, whether in the Post-pliocene period the greatest submergence of America coincided with the greatest submergence of Europe, or otherwise. It is quite possible that more accurate information on this point might remove some present difficulties. I think it much to be desired that the many able observers now engaged on the Postpliocene of Europe, would at least keep before their minds the probable effects of the geographical conditions above referred to, and enquire whether a due consideration of these would not allow them to dispense altogether with the somewhat extravagant theories of glaciation now agitated." It is hardly necessary to add that I hold and have endeavoured to prove by modern facts, in the Memoirs above referred to, that heavy icebergs borne by powerful currents, are potent agents in the production of striated surfaces and glaciated stones, as well as in transporting boulders, and that cold ocean currents are powerful eroding agents, especially when aided by heavy ice. Witness the Straits of Belle-Isle in modern times. Mr Vaughan, for many years Superintendent of the Lighthouse at that place, states that for ten icebergs which enter the straits fifty drift to the southward, yet he records that on the 30th of May, 1858, he counted in the Strait of Belle-Isle 496 bergs, the least of them sixty feet in height, some of them half a mile long and two hundred feet high. Only one-eighth of the volume of floating ice appears above water, and many of these great bergs may thus touch the ground in a depth of thirty fathoms or more, so that if we imagine four hundred of them moving up and down under the influence of the current, oscillating slowly with the motion of the sea, and grinding on the rocks and stone-covered bottom at all depths from the centre of the channel, we may form some conception of the effects of these huge polishers of the sea-floor. If this memoir had not already extended to too great length, I could have wished to notice the evidence as to the existence of ice-action in more ancient periods than the Post-pliocene. I would now merely state my belief that some of the considerations which render it necessary to invoke the action of frost and ice in the Post-pliocene period, apply also to the origin of some rocks of much higher antiquity. Ramsay has already noticed this in the case of the Permian conglomerates of England. In Canada an instance occurs in the conglomerate with boulders two feet in diameter, found in the Lower Silurian of Maimanse, Lake Superior. A still more remarkable case is that of the New Glasgow conglomerate in the coal formation of Nova Scotia, which seems to be a gigantic esker, on the outside of which large travelled boulders were deposited, probably by drift ice, while in the swamps within, the coal flora flourished and fine mud and coaly matter were accumulated.† A second indication of the existence of intense frost in ancient geological periods, is afforded by the occurrence of angular fragments of hard rocks cemented together. Such beds of angular fragments and chips, occur locally at various horizons, for example in the Upper Silurian and Lower Carboniferous in Nova Scotia, and the material of which they are composed seems precisely similar to that which is at present produced by the disintegrating action of frost on hard and especially schistose and jointed rocks. Such deposits may, I think, fairly be regarded as evidence of somewhat intense winter cold. SUPPLEMENTARY NOTE.-A visit to Nova Scotia while these sheets were going through the press enables me to add the following facts (1.) The discovery by Mr. G. F. Matthews of shells of Tellina Groenlandica in the Post-pliocene gravel at Horton Bluff, Nova Scotia. (2.) The occurrence of Laurentian boulders, probably from Labrador, in the Carboniferous region of Nova Scotia. I may specially mention a very fine boulder of Labradorite near the mouth of Carribou River, Pictou County. In Nova Scotia, however, as well as in Prince Edward Island, native stones predominate in the lower Boulder-clay, and the foreign blocks appear more toward the surface; where also, in many cases the greater part of the blocks derived from neighbouring heights are collected. I had occasion often to notice the fact, referred to above, of drift from the south as well as from the north, and also the great frequency in the boulder deposits of glaciated stones. • Can. Nat. II, p. 6. † Acadian Geology, p. 324. HISTORY OF THE NAMES CAMBRIAN AND BY T. STERRY HUNT, LL.D., F.R.S. (Concluded from page 312). III. CAMBRIAN AND SILURIAN ROCKS IN NORTH AMERICA. In accordance with our plan we now proceed to sketch the history of the lower paleozoic rocks in North America. While European geologists were carrying out the researches which have been described in the first and second parts of this paper, American investigators were not idle. The geological studies of Eaton led the way to a systematic survey of the state of New York, the results of which have been the basis of most of the subsequent geological work in eastern North America, and which was begun by legislative enactment in 1836. The state was divided into four districts, the work of examining and finally reporting upon which was committed to as many geologists. The first or southeastern district was undertaken by Mather, the second or northeastern by Emmons, the third or central by Vanuxem, and the fourth or western by James Hall; the paleontology of the whole being left to Conrad, and the mineralogy to Beck. After various annual reports the final results of the survey appeared in 1842. The whole series of fossiliferous rocks known, from the basal or Potsdam sandstone to the coal-formation, was then described as the New York system. At that time the published researches of British geologists furnished the means of comparison between the organic remains found in the rocks of New York, and those then known to exist in the paleozoic strata of Great Britain. Prof. Hall was thus enabled in his Geology of the Fourth District of New York, to declare, from the study of its fossils, that the New York system included the Devonian of Phillips, the Silurian of Murchison, and the Cambrian of Sedgwick; meaning by the latter the Upper Cambrian, or Bala group, which alone was then known to be fossiliferous. From the evidence then before him, he concluded that the Upper Cambrian was represented in the New York system VOL. VI. T No. 4. |