ABSTRACTS OF TAPERS 148 



Dqctor Grabau then presented a study of one of the factors in faunal 

 development;, which brought forth considerable discussion from Messrs. 

 Eeeds, Parks, Williston, Matthew, Ortman, Merriam, and Bassler. This 

 paper was illustrated by paleogeographic maps showing the development 

 of North America in Silurian and Devonian times. 



ISOLATION AS A FACTOR IN THE DEVELOPMENT OF PALEOZOIC FAUNAS 

 BY AMADEUS W. GRABAU 



(Ahs'fract) 



Whenever a portion of a cosmopolitian fauna is segregated in an embayment 

 of the Red Sea type, the segregated fauna being in large measure prevented 

 from intercrossing with the main stock, and so remaining true to type, develops 

 orthogenetically into a modified fauna which, when once established, remains 

 true to the new type and frequently thereafter becomes a dominant one. The 

 faunas which it is believed have thus come into existence are, among others, 

 the Brassfield fauna of the Siluric, the Helderbergian fauna of the Lower 

 Devonic, the eastern Michigan and Ontario Upper Hamilton fauna, and the 

 Ithaca fauna. Illustrations of these will be given. 



At 12.30 the Society adjourned for luncheon. 



At 2 p. m. the members were called to order by Vice-President Grabau; 

 who announced that by curtailing the longer papers somewhat separate 

 sessions would not be necessary to complete the program. 



The first paper of the afternoon session was presented by the Secretary 

 for the author and dealt with new discoveries in the early Paleozoic rocks 

 of Alaska. 



AN ORDOVICIAN FAUNA FROM SOUTHEASTERN ALASKA 

 BY EDWIN KIRK 



(AI)s'tract) 



The oldest fossiliferous sediments hitherto known in southeastern Alaska 

 were of Silurian age. The discovery last season of early Ordovician sediments 

 is therefore of considerable interest. 



Extending along the shore for a considerable distance to either side of the 

 town of Wrangell is a great series of highly metamorphosed sediments. These 

 consist almost entirely of greenstones, crystalline schists, and argillites. A 

 block of fossiliferous slate was found near Wrangell by Prindle some years 

 ago. These fossils were reported by Girty as being anything from Devonian 

 to Recent in age. If Paleozoic, he suggested that the age was probably De- 

 vonian or Carboniferous. The fossils were in a very poor state of presen-a- 

 tion, and the prevailing opinion has been that the block of slate was an erratic. 

 The beds at Wrangell have generally been assigned to the mainland belt of 

 supposed Carboniferous-Mesozoic, that ranges from the Ketchikan area at the 

 south to the .Tuneau and Chilkat areas at the north. 



