We are indebted for the material from which the following notes have been compiled to Principal Dawson, of Montreal, and to the Secretary of the Portland Society of Natural History, to whom our best thanks are due for the opportunity thus afforded us of comparing the fossils of the North American Clay Beds with those of our own country. By carefully washing theclays kindly forwarded to us, we have obtained many specimens in excellent condition for examination.
POST-TERTIARY ENTOMOSTRACA.of the beds we have exammed. Shell-beds have also been found, under circumstances needing special local examination, intercalated between masses of Boulder Clay of the same character.The only cases in which a Boulder Clay physically analogous to that of which we are treating contains fossils are those which will presently be described as a second type of Boulder Clay, which forms cliffs near the shore and never extends beyond a few miles inland.Whatever explanation of its origia may be given, so far as present investigations extend, there seems to be ample evidence for the existence of a Boulder Clay : (I) Older than the stratified clay containing Arctic shells ;(2) extending to far greater heights than either any fossiliferous Boulder Clay or any stratified clay ; (3) unsubjected to any action of the tidal wave upon the shore ; (4) and connected with the more remote and extreme Arctic conditions of the Glacial Epoch.T/ie position of the beds from which we have obtained Ostracoda in relation to this Boulder Clay will at any rate furnish a guide available for the practical use of the advocates of any theory regarding their succession, which may be in debate.II. There oxii fossiliferous Boulder Clays which have several striking peculiarities.1. They occur (so far as we yet know) either close to the coast or within a distance of four or five miles, and generally form low cliffs immediately on the shore. They may be seen on the north-east coast of Scotland, along the north-east coast of Ireland, on the north-east coast of England, on the Lancashire coast, and along the banks of the Mersey.2. The shells they contain are very seldom perfect, except in the case of a univalve, like Turritella communis ; and, even when perfect, they are not found in their natural living position.These features form a remarkable contrast to the state of the fossils in the great shelly beds resting upon the Boulder Clay in the Clyde districts. In those beds mimerous specimens of such Molluscs as Saxicava {Pano^aa) Norveyica, and Mya TJddevallensis are foimd in their natural upright position, with fragments of the syphon preserved ; while Fecten Isla7idicus, Astarte sulcata, and almost every other bivalve, together with the Ostracoda, occur with united valves ; and in many cases, when they are taken freshly from the clay, the connecting ligament may be detected, although it quickly decays on exposure to the air.3. The fauna is sometimes less Arctic in character than that yielded by the stratified glacial clay immediately resting upon the lowest unstratified Boulder Clay. TheCaithness Boulder Clay, which reaches a thickness of more than 100 feet, contains (writes Mr. Jamieson) "remains of sea shells all through it, often from top to bottom, and these shells are broken, rubbed, and scratched, evidently by the same agency that marked the rocks and boulders," while " the group is the most modern, except that of Cytheridea punctillata, Brady.Xestoleberis depressa, G. O. Sars.Cytherura undata, G. 0. Sars. Cytherideis sub...
UNDER the general term, Boulder Clay, many deposits produced at various periods during the great glacial epoch, and by different causes, have been loosely included. It is necessary to distinguish between these various "Boulder Clays," before observers in separate localities will be able to understand each other's language, and before any satisfactory theories can be established regarding the methods, of their formation.The old motto for statesmen dealing with barbarous tribes on the frontiers of an empire was, "Divide and command;" and this must also be the motto for students of the apparently confused accumulations of glacial deposits. We must divide to command. I. The oldest boulder clay I at present believe to be represented by that which underlies the shell clay of the West of Scotland.It is only in the lower districts, however, that the shell clay rests upon it, while it reaches to a height in Scotland (1,500 feet or more) far beyond that at which any shells have yet been dis covered. Its thickness extends from a mere covering of the rock, to the depth of even 300 feet, and is excessively variable.It is closely compact, as though subjected to immense pressure, and difficult to work even with the pick-axe.Although occasionally containing patches of sand, of greater or less extent, it has no stratification. The included stones are in large numbers, polished and striated, and have not been broken by the process through which they have passed. Even thin and brittle pieces of shell are found finely striated.These polished and striated surfaces are so freshly preserved that the stones could not have been rolled on a beach subsequently to their production. Any trituration would at once destroy the fineness of the glaciated surfaces.The included stones are chiefly traceable to the heights nearest the locality in which the special bed is found, although a certain proportion have travelled from distances in the direction along which a glacier would naturally have moved, according to the general conformation of the country.This boulder clay, we suggest, belongs to the period when the cold of the glacial epoch reached its intensest point. University on June 25, 2015 at Brigham Young http://trngl.lyellcollection.org/ Downloaded from 1 See a joint account of these beds by Dr. Bryce and the writer, " Geology of Airan."-P. 166,2nd edition. University on June 25, 2015 at Brigham Young http://trngl.lyellcollection.org/ Downloaded from V. Conclusion, Bearing of modern denudation upon the value of geological time. University on June 25, 2015at Brigham Young http://trngl.lyellcollection.org/ Downloaded from
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