1916] 



The Ottawa Naturalist. 



123 



Centtal Nsw York 



Eastern New York 

 (Chenango Valley) 



Chsm'jng 

 ■fc-malion 



Porlage 

 formalion 



Spirii'er d'ijunclu; I'oun.i 



Tropidoleptus 



Buchic'a retro£lii;'.i fcuna 



■fully l.meslone y^^^^^ ' " ~ ~'- ' 



Kamilion j 

 fomiatior; "j 



Tropidoleptus carinalus fauna 



20 



30 



40 



50 Miles 



Fig. 2. A diagrammatic east-west cross-section of the Middle and Upper Devonian of 



southern New York, showing the relations of Tropidoleptus carinatus to the western faunas 



during Portage and Chemung time. Total thickness of the section is about 2,700 feet. 



The presence of a recurrent Hamilton species like Tropi- 

 doleptus carinatus in the Chemung fauna of southern New York 

 involves its withdrawal from at least the major part of the New 

 York area at the end of Hamilton sedimentation to some part 

 of the sea furnishing a more congenial environment than that 

 which accompanied Genesee and Portage sedimentation. In 

 the newly adopted habitat, or in a small portion of the old one, 

 it fotmd a haven where those conditions of the Hamilton sea 

 which were essential to its life were maintained throughout 

 Genesee and Portage time. With the initiation of Chemung sedi- 

 mentation T. carinatus extended its habitat back again over a part 

 of the area which it h'ad previously occupied, as shown in fig. 2 . 



These recurrent faunas furnish convincing evidence of the 

 existence during the Palaeozoic of distinct faunal provinces. 

 It seems safe to conclude that the recurrence of a fauna has 

 been due to the oscillation or migration of the factors which 

 conditioned its geographic distribution. 



Palaeogeography is a field of knowledge to the extension 

 of which the collection of fossils contributes most important 

 data,. Collections which will contribute most to this subject 

 are those concerning which the collector has supplied, in addi- 

 tion to the data already mentioned under methods of collecting, 

 complete data regarding the physical features of the rocks in 

 which they are found. This physical data should indicate very 

 fully the nature of the sediments associated with individual 

 fatmules, as to composition, texture, hardness and colour. The 

 collector should note the character of the lamination, whether 

 in thin or thick sheets or variable, and whether uniform or 

 alternating composition characterizes the beds. The presence 

 or absence of cross bedding, ripple marks, current marks and 



