FURTHER STUDIES OF CAMBRIAN GEOLOGY 

 IN THE ROCKY MOUNTAINS 



By CHARLES E. RESSER, 



Curator, Di7'ision of Slrai!(/rapliic Polroiitology, U. S. National Museum 



The record of life in the Caml)rian rocks of the Rocky Mountains, 

 dating- from almost the very beginnings of biological history, is 

 slowly being revealed through the researches of geologists, and to the 

 fact that the record goes back so^ far must be attributed the wide- 

 spread interest in each new item uncovered. I was afforded the 

 privilege during the field season of 1929 of continuing- my studies of 

 these ancient rocks and their contained fossils. My primary interest 

 and effort, however, was directed not so much towards the discovery 

 of new things but towards gathering- data that will serve in systema- 

 tizing- our existing knowledge, for although much information and 

 many fossils have been accumulated, these are not yet sufficiently 

 digested to be generally available in a usable system. 



As in past seasons. I used an auto truck and outfit that had been 

 stored at the central location of Salt Lake City. Leaving there late 

 in June, my assistant and I moved northward toward our chosen 

 field in Montana. A pleasant feature of this year's work was that we 

 were twice accompanied by Luciano Jacques de Moraes. a geologist 

 of the Brazilian Geological Survey, who was visiting this country. 

 He met us at Salt Lake City, and as several of our interests coincided, 

 particularly the study of algal deposits, he accompanied us as far as 

 the Yellowstone National Park. In the Park and along the route to 

 it. we frequently stoi>ped to study such de]:)Osits. obtaining much inter- 

 esting information and some instructive specimens but also raising a 

 new set of problems. For instance, last spring the rotogravure pic- 

 torial section of several eastern Sunday newspapers printed pictures 

 of a large undercut boulder in the Gibbon River, several miles below 

 the Norris Geyser Basin in the Park. We reexamined this boulder 

 and found that its peculiar pedestal structure is due to the fact that its 

 base is tightly cemented to the river bed by algal deposits, which pre- 

 vents its turning over and therel)y being rounded in the usual manner. 

 But the unsolved problem raised is why algae should make a perfect 

 concrete pavement for the river over the rapids at this point while 

 both above and below no such lime deposition is taking place. 



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