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168, be it palæontological, geographical or stratigraphical, to show that these Devonic red beds were laid down in lakes. The attempt to prove this theory has, as is so often the case in the development of science, led to careful observations by many men, to the formulation of alternative theories and to the collection of a great mass of valuable data. That the first theory may perhaps prove incorrect is of small importance compared to the fact that it made geologists realize that there was a problem to be solved, and spurred them on to its solution. This lacustrine theory, however, has had a longer life than is usually allotted to first theories, for it has held on to the present day and still has more adherents than has any later hypothesis. The monograph by Sir Archibald Geikie "On the Old Red Sandstone of Western Europe," published in 1878, embodied such an elaborate discussion of the various lakes of the Devonic period and so many field observations were adduced to back up the theoretical statements that later writers have with few exceptions considered that the lacustrine origin for the Old Red sandstone was proved beyond any further question. To be sure, one or two heretical geologists have raised objections to these ancient lakes and have preferred to think that the Old Red was a marine deposit formed under particular and inimical conditions. Within the last ten years both of these interpretations have been questioned by not a few, and although the majority of geologists unhesitatingly accept the older ideas, particularly favoring the lacustrine theory, nevertheless, there is an everincreasing tendency at the present time to recognize the fact that all continental formations need not necessarily be deposited in large bodies of standing water. Thus the ultra-modern school of geologists champions the importance of fluviatile deposits in the past, insisting especially upon the fact that such deposits are spread out in large part on the land and not in lakes or inland seas. This school of "terrestrial" as opposed to "aqueous" geologists, found its earliest leaders in Johannes Walther and Albrecht Penck, later disciples in this country being Professors Grabau and Barrell. The last two as well as Walther and Goodchild have argued the dominantly continental origin of the Old Red sandstone, Professor Grabau arguing On the basis of the field evidence and on lithological and palaeontological grounds; and Professor Barrell from the standpoint of the physical conditions which must have prevailed at that time. These various theories will presently be taken up and the evidence for each will be discussed.