234 FROM FISH TO PHILOSOPHER 



the sea, from which terrestrial forms had emerged across 

 the tidal strand. Favoring this presumption was the cir- 

 cumstance that those Devonian beds in which the oldest 

 fish fossils are found in greatest abundance were ac- 

 cepted to be marine in origin. However, geologists had 

 come to realize that much of the Old Red Sandstone 

 (or Devonian) of the British Islands was of fresh-water 

 origin, and spoke of it as having been laid dovm in 

 *fresh-water lakes' or *inland seas'— an equivocal descrip- 

 tion that failed to stimulate paleontological reinterpreta- 

 tion since it was conceived that the ancient fishes could 

 have migrated transiently into brackish estuaries and 

 even into fresh-water lakes. 



A complete reinterpretation of this problem was first 

 suggested by T. C. Chamberlain in 1900 {30}, who 

 pointed out that the earhest known vertebrates were 

 predominantly confined to sediments of established or 

 suspected fresh-water origin, along with the remains of 

 land plants and fresh-water molluscs, and strangely ab- 

 sent from the indubitably marine deposits. Noting that 

 the typical vertebrate pattern is uniquely fitted to propel 

 the animal against a moving stream, he proposed that 

 the earliest vertebrates had been evolved in the fresh 

 waters of the continents. 



In the decade following Chamberlain's paper the fresh- 

 water origin of the Old Red beds was increasingly ac- 

 cepted by geologists, and more attention was given to 

 the conditions of their deposition. The biological aspects 

 of this problem were reviewed in igi6 by Barrell {26, 

 27} who had himself contributed importantly to the geo- 

 logical interpretation of the Old Red deposits. It was 

 Barrell's view (which is still accepted with minor quali- 

 fications) that much of this red sandstone had been 

 laid dovra, not in quiet bodies of water such as lakes, 

 estuaries, or inland seas, but in wide, torrential rivers 

 draining the great mountain ranges of the Devonian 

 continent. In a chmate marked by alternation of extreme 

 dry seasons and torrential rains, the uplands were sub- 



