1911] The Ottawa Naturalist. 15 



SUMMARY OF A LECTURE DELIVERED, BEFORE THE 



OTTAWA FIELD-NATURALISTS' CLUB, ON JAN. 



28th, 1911, BY DR. PERCY E. RAYMOND. 



The subject of the talk, the "Local Geology," had been so 

 often and so admirably treated before the Society, that the 

 speaker did not attempt to repeat the details of the local distri- 

 bution of the rocks and fossils, but made the local section the 

 basis of a brief exposition of what has been recently accom- 

 plished in mapping the ancient geography of the region. The 

 older view, that throughout Ordovician time the Ottawa valley 

 was continuously an arm of the sea has been modified in recent 

 years by critical studies of the fossils, and the speaker endeavour- 

 ed to show the great value of fossils in studying the former 

 distribution of lands and seas. It was pointed out that at the 

 present time the fauna of the Pacific Ocean was very different 

 from that along our eastern coasts, and*that it had been found 

 that the fossils showed similar differences in contemporaneous 

 faunas living in separated ocean basins. The two great basins 

 which had affected this region were the Atlantic and the great 

 interior sea. 



The most ancient fossiliferous sedimentary rocks, the lower 

 Cambrian, do not seem to have been deposited in this region, 

 though an arm of the sea passed through the St. Lawrence and 

 Champlain valleys at- this time. During a large part or all of 

 Middle Cambrian time, both the Ottawa and Champlain regions 

 were above sea level, and the next inundation, the first to reach 

 Ottawa, came from the Gulf of Mexico. In late Upper Cambrian 

 time, however, the sea seems to have broken through to the 

 Atlantic in the St. Lawrence valley, for at Levis we have a 

 mixture of interior and European tvpes of fossils. At this time 

 the water was very shallow in the Ottawa valley, and the arm 

 of the sea was probably in the form of a bay opening to the east- 

 ward. In this bay was deposited the Potsdam sandstone. 



During the early part of Beekmantown time the Ottawa 

 region was again above the water level, but toward the later 

 part, the sea to the eastward again encroached upon the land, 

 bringing in a part of the Upper Beekmantown (Ft. Cassin) fauna. 

 As the land was submerged, the sea seems to have at first derived 

 a large part of its sediment from the more ancient Potsdam sand- 

 stone, thus forming the so-called passage beds of Potsdam sands 

 with Beekmantown fossils. 



After Beekmantown time there was a general emergence of 

 the Ottawa and Champlain valleys, and the Ottawa region was 

 land until the latter part of Chazy time. The Chazy sea was an 



