94 R. A. Daly — Limeless Ocean of Pre-Canibrian Time. 



dary the sedimentary series is no less remarkable for its almost 

 absolute failure to carry other fossil shells or skeletons. Dur- 

 ing- the summer of 1906 the writer secured evidence that the 

 Siyeh formation in Montana is stratigraphically equivalent to 

 the main division of the Castle Mountain limestone in Alberta, 

 and is therefore of Cambrian age ; but this evidence, while 

 very strong, is based entirely on the lithological similarity of 

 the two formations and of the respective underlying forma- 

 tions. Willis, Weller and Walcott have all carefully searched 

 for fossils in the Siyeh dolomite, limestone and argillite as well 

 as in the associated rocks, but have met with almost no suc- 

 cess, except in the Beltina horizon (Altyn limestone), as alread}* 

 noted. Considering their age and relations, these rocks are all 

 singularly free from signs of important dynamic metamorphism. 

 As the writer has worked, season after season, on the magnifi- 

 cent sections exposed along the forty -ninth parallel, the failure 

 to find fossils anywhere through thousands pi feet of the most 

 likely looking shales and limestones, has itself become a geo- 

 logical problem. 



Explanations of the Unfossiliferous Character of pre- Cambrian 



Sediments. 



1. Hypothesis of the metamorphic destruction of fossil 

 remains. — The view that shells or skeletons were actually once 

 present in anything like the proportions characteristic of Silu- 

 rian or later marine sediments, and have since been destroyed 

 through either static or dynamic metamorphism, has proved as 

 unsatisfactory for these pre-Silurian American terranes as it 

 has for pre-Silurian terranes throughout the world. The 

 opposed hypothesis that the hard parts of marine animals were 

 seldom entombed in pre-Cambrian strata is worthy of careful 

 examination. This latter hypothesis is multiple, since it may 

 postulate different causes for the lack of entombment. All 

 postulates must, however, recognize the fact that the mechani- 

 cal conditions of burial and preservation were all present. So 

 far as chemical composition, detrital composition, rapidity of 

 deposition, etc., are concerned, the sediments of the Cordil- 

 leran province, as of other pre-Cambrian formations, are ideal 

 for perfect fossilization. 



2. The Brooks hypothesis. — The admirable essay of W. K. 

 Brooks in the Journal of Geology (vol. ii, 1894, p. 455) states 

 one conceivable hypothesis. He suggests that the photobathic 

 zone of the sea, including the bottom, first became inhabited 

 just before Cambrian time. He cousiders it probable that all 

 the fundamental types of animals from protozoon to mollusc 

 and arthropod, but all as yet soft-bodied, had been evolved in 

 the surface waters of the open sea, far from land. At the 



