444 CARNEGIE INSTITUTION OF WASHINGTON. 



in the remaining chapters of the same pubhcation. In this study the 

 earher series of publications by the same author on the morphology of 

 the Permo-carboniferous vertebrates of North America was taken as 

 establishing the character of the organisms discussed and an attempt 

 was made to restore the elements of the organic and inorganic environ- 

 ment. 



One important result of the attempt to prepare a concrete illustra- 

 tion of these principles was the development of the conception that the 

 similarity of organisms, or the homotaxial equivalency, may be de- 

 termined by the environmental conditions independent of time equiv- 

 alence, and that a propagation of environmental conditions, practi- 

 cally unchanged, across a considerable geographical area may carry 

 with it a nearly identical fauna or flora, even though these conditions 

 may, without break, successively transgress two or more distinct inter- 

 vals of geologic time as determined by diastrophic criteria. This 

 has been illustrated by an occurrence in the late Paleozoic, described 

 in publication No. 283 of the Carnegie Institution. 



It is obvious that work of this character can only be carried forward 

 to the best results by the cooperation of a group of men, specialists 

 in different fields, who will attack a definite problem from its various 

 angles and by compilation and analysis of their results eliminate erro- 

 neous assumptions and results and produce positive results by a corre- 

 lation of all the parts. Such a plan has been proposed to the Carnegie 

 Institution in the suggestion for a department of palseogeography, and 

 an effort is being made at present to solve certain elements of the 

 problem by the committee upon sedimentation. 



Under the grant it was proposed to carry out the studies in North 

 America and then extend them to other regions of the world. The 

 portion deahng with North America has been completed and pubhshed 

 and a large amount of information has been accumulated concerning 

 the late Palaeozoic in other regions. The disturbed conditions caused 

 by the Great War prevented contemplated visits to these other regions 

 and the funds of the grant have been extended over a longer period 

 than was contemplated originally and have been applied to researches 

 in North America that were suggested in the course of the work. 



One of the most interesting questions which has arisen is the appar- 

 ently sudden extinction of the peculiar Permo-carboniferous verte- 

 brate fauna of North America and the equally abrupt appearance of 

 the late Triassic vertebrate life, in beds which are apparently contin- 

 uous in deposition but barren of all traces of vertebrate life in the 

 interval between the deposition of the remains of the two faunae. 

 In only one or two localities can a separation be made between the 

 terrestrial deposits of the two periods by diastrophic criteria. Work 

 was diverted to a search for a continuation of the Permo-carbonif- 

 erous fauna in North America, as it continues in Europe and South 



