178 THE HABITAT OF THE EURYPTERIDA 



cation fissures and other structural features to be mentioned below 

 was taken as indicative of the mud flats along shore, which were from 

 time to time inundated by the waters of the lake. Plant, insect, 

 and crustaceous remains, as well as the abundant fish fauna, were 

 correctly pointed out as showing the near presence of land. The 

 distinctness of the fish and merostome faunas in the Caledonian and 

 Orcadian rocks was cited as proof of the distinctness of the lakes in 

 which these organisms had lived. It is surprising, and therefore, 

 worthy of note, that Geikie came so very near to the recognition of 

 the Old Red fish and eurypterids as river dwellers that one marvels 

 at his not having reached that conclusion. The arguments which 

 he cites to account for the differences of the ichthyic fauna of his 

 Lake Orcadie and Lake Caledonia, which were supposed to have been 

 separated by the Grampians, are illustrations taken from modern 

 river faunas; and, if application were made directly to the Old Red 

 faunas, one would have to say that the fish in the two Devonic lakes 

 were different because they came from rivers whose headwaters were 

 separated by a divide. I shall give Geikie's statement in order to 

 show how near he came to the discovery that the Old Red Fauna 

 came from the rivers, and how he failed to realize this because he was 

 so intent on the theory of lakes. 



"In the second place," he says, "there does not seem to be any 

 valid reason why the ichthyic fauna of two adjacent but completely 

 disconnected water-basins should not have differed considerably in 

 Old Red Sandstone times, as they do at the present day. Even in 

 the same river-system it is well known that the fishes of the higher 

 portions of the basin are sometimes far from corresponding with those 

 in the maritime parts of the area. Neighboring drainage-basins, 

 divided by a comparatively unimportant watershed, sometimes show 

 a remarkable contrast in their fishes. This has been well pointed 

 out by Professor E. D. Cope, in a suggestive paper "On the Distribu- 

 tion of Fresh-water Fishes in the Alleghany Region of South-western 

 Virginia." 13 The James and Roanoke rivers descend the eastern 

 slope of the continent and discharge into the Atlantic. In their upper 

 waters they have only four species of fish in common. In the upper 

 waters of the rivers Holston and Kanawha, which flow south-west- 

 wards into the Mississippi basin, there are only two species alike. 

 Between those eastern and western pairs of rivers runs the more 

 marked water-parting of the Alleghany chain. Out of fifty-six species 



13 Journ. Acad. Nat. Sci., Philadelphia, vi, 2d series (1860-69), p. 207. 



