334 SCIENCE PROGRESS 



formations which formerly were vaguely said to be of "estuarine" or "brackish 

 water " origin. 



It has been left to an acute American geologist, Prof. Joseph Barrell of Yale 

 University, to extend these views in great detail to a British formation. The 

 Old Red Sandstone, first thought by Hugh Miller to be of marine origin, and still 

 so regarded by P. Macnair, has long been attributed by the majority of geologists 

 to deposition in great freshwater lakes. This view, originated by Fleming and 

 Godwin-Austen, was adopted and developed by Sir A. Geikie, and owes its great 

 vogue to his authoritative advocacy. Prof. Barrell now interprets the Old Red 

 Sandstone as a typical continental deposit mainly of fluviatile origin, arising 

 in a region of seasonal rainfall in which alternations of semi-arid and rainy 

 conditions were the rule, with probably longer periods of drought than of humidity. 

 While this is the first detailed study of the Old Red Sandstone from this 

 point of view, several British investigators have already reached the same stand- 

 point, especially Dr. C. B. Crampton and Mr. R. G. Carruthers in the new 

 Caithness Memoir of the Scottish Geological Survey (1914), which Prof. Barrell 

 has evidently not seen. These authors clearly recognise the continental nature 

 of the Old Red Sandstone and the fluviatile origin of many of its sediments, but 

 they have obviously been hampered in accepting the full consequences of this 

 view by their manifest reluctance to discard the Lake Orcadie of Sir A. Geikie. 

 In other recent Scottish Geological Survey memoirs Mr. E. B. Bailey and 

 H. B. Maufe have approached the theory of fluviatile origin, and Prof. J. W. 

 Gregory in his Geology of To-day (191 5, p. 204) has ascribed the Old Red 

 Sandstone to conditions similar to those which have produced the widespread 

 sheets of gravel known in New Zealand as " shingle rivers." The late J. G. 

 Goodchild in 1904 came very close to the fluviatile view, as is indeed acknow- 

 ledged by Barrell. He regarded the Old Red Sandstone as accumulated under 

 continental conditions, partly in large inland lakes, partly as torrential deposits 

 of various kinds, partly as desert sands, and partly as the results of extensive 

 volcanic action. The fluviatile deposition advocated by Prof. Barrell is inter- 

 mediate between torrential and lacustrine, yet quite distinct from either, and may 

 include subordinate deposits of torrential, lacustrine, or desert origin in different 

 parts of the basin of accumulation. Dr. R. Campbell, in a recent account of the 

 geology of south-eastern Kincardineshire {Trans. Roy. Soc. Edinburgh^ 191 3, 48, 

 954), recognises the torrential origin of the great conglomerates of the Lower 

 Old Red Sandstone, but regards the finer conglomerates, sandstones, and shales 

 as having been accumulated in a large, shallow, freshwater lake, or chain of lakes. 

 The criteria relied upon by Barrell for the establishment of the theory of 

 fluviatile origin are chiefly the great extent, thickness, and coarseness of the 

 conglomerates, and the great vertical and areal distribution in the finer sediments 

 of marks of exposure to the air ; but there are numerous supporting lines of 

 evidence. He recognises the inadequacy of certain characters, such as ripple- 

 marks, cross-bedding, absence of fossils, and presence of red or variegated beds, 

 when taken by themselves, as criteria of origin, since all of these may occur under 

 a variety of conditions. It is the concurrence and quantitative development of 

 certain lithological and structural features, together with stratigraphical and 

 palasontological characters, which are to be regarded as diagnostic of certain 

 modes of origin. 



The thick and extensive gravel deposits of the present day are being laid down 

 at the foot of mountain ranges by torrents, and on the upper parts of great river 

 flood-plains. No thick marine gravels are known, and the thickness of coarse 



