362 SCIENCE PROGRESS. 



in a paper on the Devonian of the Eastern Alps (24). A 

 valuable account of the Devonian rocks of Spain is given 

 by Barrois (25), who compares them with their equivalents 

 in other areas. The adoption in America of the line of de- 

 marcation between Silurian and Devonian, suggested by 

 Schmidt, would settle the vexed question of the age of the 

 lower Helderberg group. Its lowest subdivision, the Water- 

 lime group, with Eurypterus Fischeri would thus constitute 

 the top of the Silurian system, whilst its four upper members 

 would be lower Devonian. The minute classification of 

 these American beds will probably be a work of some diffi- 

 culty, owing to the variations in their character in different 

 regions (26). When it is made, no doubt a much more suc- 

 cessful comparison can be instituted between the European 

 and American beds. 



The recent work amongst the Devonian rocks shows 

 that in their case, as in that of the lower Palaeozoic rocks, 

 not only are palaeontological characters of definite sub- 

 divisions in many respects identical over wide areas, but 

 also lithological characters. This is especially well seen in 

 the case of the upper and middle Devonian limestones. 



5. CARBONIFEROUS AND PERMIAN SYSTEMS. 



Although the rocks of these systems are so strongly 

 separated from one another in Britain, it is well known 

 that this separation is only local, and as the carboniferous 

 insensibly pass into those of the Permian system else- 

 where, it will be advantageous to treat of the two systems 

 together. 



An idea seems to have grown up in the minds of British 

 geologists that the marine deposits of carboniferous age are 

 not separable into zones comparable with the graptolite 

 zones of the lower Palaeozoic rocks and the ammonite zones 

 of the mesozoic strata, and it has been inferred that the 

 carboniferous rocks accumulated too rapidly to allow the 

 differentiation of successive faunas. Modern research 

 points to the conclusion that this view is erroneous, and, as 



