108 PROCEEDINGS OF THE AMHERST MEETING 



not necessarily support the claim, so often made, that since at the beginning 

 of Cambrian time life was already nine-tenths differentiated ; biotic develop- 

 ment spans an interval ten times as long as that which has elapsed since that 

 date to the present day. In organic expansion there are grave crises wherein 

 growth and change are accelerated more in brief episodes than those which 

 take place in the millions of years which lie between. The intellectual devel- 

 opment which took place since mid-Tertiary times and the rapid structural 

 changes which transpired when the land fauna was established are well known. 

 An earlier and more important crisis was, as Brooks points out, the discovery 

 by life of the bottom of the sea. Bearing this feature in mind, the inferential 

 immensity of the pre-Cambrian time-span is immeasurably cut down. Before 

 the Proterozoic and Archeozoic eras, there was, perhaps, a single other Eozoic 

 era of which we do not yet take definite cognizance, of equal length, before 

 reaching the Azoic chaos. According to the best revised estimates, therefore, 

 500,000,000 years have elapsed since life on our planet was originally initiated 

 or created. 



Presented by title in the absence of the author. 



QUANTITATIVE STUDY OF THE DERIVATION OF NORTH AMERICAN 



ALGONKIAN SEDIMENTS 



BY ARTHUR C. TROWBRIDGE AND WALDO S. GLOCK 



(Abstract) 



An attempt to test quantitatively the usual statement that North American 

 Algonkian sediments were derived from the erosion of North American Algon- 

 kian lands underlain by Archean rocks results in the conclusion that about 

 11,000,000 square kilometers of land surface must have been degraded to an 

 average depth of about 8,400 meters, to account for the free quartz found in 

 Algonkian sediments. The paper describes the methods used, under several 

 different assumptions of depositional and erosional areas, etcetera, in arriving 

 at this general conclusion. The results of the estimates are discussed in terms 

 of plural erosional cycles and the duration of Algonkian times. 



Presented by title in the absence of the authors. 



CAMIiRO-ORDOYJCJAN SECTION NEAR MOUNT ROBSOX, WESTERN CANADA 



BY LANCASTER D. BURLING 



(Abstract) 



The Cambrian and Ordovician of the Mount Robson region have been de- 

 scribed as comprising the following eleven formations: Robson (Ordovician) ; 

 Lynx (Upper Cambrian) ; Titkana, Mumin, Hitka, Tatay, and Chetang (Middle 

 Cambrian) ; and Hota, Mahto, Tah, and McNaughton (Lower Cambrian). 



Detailed sections prove that the mountains adjacent to Mount Robson expose 

 strata differing from those which the earlier reports would lead us to suppose. 

 The more important of the necessary corrections are: (a) Mount Robson, de- 

 scribed as exposing in its summit 3,000 feel of Robson limestones above the 



