GEOGRAPHY OF BRITISH ISLES IN DEVONIAN TIME 349 



mode of origin of the continental Tertiary deposits : once looked on as 

 deposited in lakes greater in area than any now existing on the earth, 

 they are now regarded as accumulations made chiefly on river plains. 

 Such a reinterpretation for the Old Eed Sandstone involves radical 

 changes in the conceptions of Devonian geography — no less a change than 

 the substitution of land surfaces, occasionally flooded, as a replacement 

 in the mental vision of wide and permanent bodies of water. If the new 

 interpretation is well founded, it means that such terms as "Lake Cale- 

 donia" and "Lake Orcadie" should be turned into the "Caledonian and 

 Orcadian basins/' 



Peevailing Views regarding Conditions of Origin 



Hugh Miller regarded the Old Eed Sandstone as a marine deposit, 

 reaching this conclusion by direct comparison of the structures of the 

 solid rocks with near-by tidal deposits now being made. It was soon per- 

 ceived, however, by British geologists that the sediments and organic 

 contents were of different types from the obviously marine Devonian 

 strata to the south. These distinctions led Godwin-Austen in 1855 to a 

 view, previously maintained by Dr. John Fleming, that the Old Red Sand- 

 stone was laid down in great fresh-water lakes or inland seas. This in- 

 terpretation soon became generally accepted- During the next generation 

 the geologist who gave most thorough study to the subject was A. Geikie. 

 He separated the Old Red Sandstone into several basins of deposition. 

 According to Geikie, Lake Caledonia stretched across central Scotland, 

 and within it were deposited a maximum thickness of perhaps 20,000 

 feet of strata. Other basins were occupied by the Welsh Lake. Lake 

 Cheviot, Lake Lome, and Lake Orcadie. In the latter area there are 

 exposed as much as 16,000 feet of strata. These views are developed in 

 his paper of 1877-1878 4 and are summarized in his textbook in 1903. 



Macnair and Reid in 1896 give, however, what they regard as reasons 

 for holding that the fresh-water lake hypothesis of origin is "utterly 

 untenable" and come back to the view of Hugh Miller, that the Old Red 

 Sandstone is marine. 5 



In 1904 Good child published a paper which embraces the following 

 statements : 



"There is no satisfactory reason for regarding any of the Scottish rocks of 

 Devonian age as of marine origin ; and, on the other hand, there is much to be 

 said in support of the view that they were all formed under continental con- 



4 On the Old Red Sandstone of western Europe. Trans. Roy. Soc. Edinburgh, vol. 

 xxviil, pt. ii, pp. 345-452. 



6 Geol. Mag., Decade 4, vol. iii, 1896, pp. 106-116, 217-221. 



