444 GEOLOGY. 



to the history of Devonian deposition than the corresponding strata 

 of the Rhine basin. Igneous rocks are often associated with the sedi- 

 mentary beds, and valuable ore-bearing veins sometimes result, as in 

 Devon and Cornwall. 



The second phase of the Devonian is the Old Red sandstone. This 

 great series overlies the Silurian and underlies the Carboniferous. 

 Its stratigraphical position is therefore clear, and it is thought to repre- 

 sent the Devonian. This phase of the Devonian is widely distributed 

 in Wales, in west and north England, Scotland, in the Orkney and 

 Shetland Islands, and in Ireland. It is possible that certain beds of 

 Norway, doubtfully referred to the Devonian, are to be correlated 

 with the Old Red sandstone phase of the Devonian in the British 

 Isles. The same phase of the formation likewise re-appears in western 

 Russia. 



Concerning the history of the Old Red sandstone there has been much 

 difference of opinion, but it is commonly held to have been deposited in 

 a series of inclosed or nearly inclosed basins containing lakes or inland 

 seas, the waters of which were fresh or brackish. It is further believed 

 that crustal warping gave the sea occasional access to these basins. 

 These conclusions are based on the nature of the formation, and on 

 the testimony of its fossils. In general the strata are poor in fossils, 

 and those which are present indicate that the waters in which the 

 strata containing them were deposited were not the waters of the 

 open ocean. Some of the fossils are fresh-water species, while others 

 are land species. At some horizons, however, marine species occur. 

 It is not improbable that some portions of this singular series are of 

 subaerial, rather than subaqueous origin. 



Against this interpretation several objections have been urged. 

 In the first place, the presence of occasional marine fossils is thought 

 by some to be against the inclosed-basin hypothesis. 1 The answer 

 to this objection has already been suggested. A second objection 

 is found in the wide extent of the formation, if it be referred to a single 

 body of water. As partially meeting this objection, it is said to be 

 probable that there was not a single inclosed sea or lake in which 

 these beds were deposited, but rather many inclosed basins, and that 

 no one was necessarily very extensive. Neumayr 2 also finds a diffi- 



1 Kayser and Lake, Text-book of Comparative Geology. . 



2 Neumayr, Erdegeschichte, Vol. II, 1st ed. 



