ABSTRACTS OF PAPERS 107 



at Manitou, Colorado. The dark brownish red limestone of that section is a 

 thin bed at the base of the Manitou, resting on the brown siliceous rocks of 

 the Tawatch sandstone or quartzite. It has been somewhat doubtful whether 

 this red 'limestone bed should be assigned to the Manitou or to the Tawatch. 

 Its upper surface is somewhat irregular, suggesting that it was followed by 

 an erosion interval which would give time for the weathering regional by Dr. 

 Galloway's explanation of the origin and limestone. Under this conception, 

 the red limestone bed in question belongs to the Tawatch cycle of sedimenta- 

 tion rather than to the Manitou. 



Dr. Bassler : In the discussion of the Clinton iron ore, I called attention to 

 the fact that the thickest beds of such ore in the Appalachian district are in 

 areas where the underlying red beds of Upper Ordovician age are either very 

 thin or are entirely eroded away, thus seeming to indicate the sedimentary 

 origin of the ore from preceding deposits. 



PETROGRAPHIC STUDIES OF SOME NEW YORK SEDIMENTS 

 BY HAEOLD L. ALONG 



(Abstract) 



The purpose of this paper, written for the stratigraphic paleontologist, is to 

 call attention to the confirmatory and supplementary aid the petrographic 

 microscope can furnish to students of normal sedimentary rocks. The instru- 

 ment is of value in determining the conditions of deposition and manner of 

 accumulation of clastic materials, thereby supplying information for the paleo- 

 geographer in his attempts to reconstruct the shorelines of ancient seas. The 

 geologist working with highly metamorphosed sediments needs more informa- 

 tion regarding normal sediments than is now available. 



No difficulty is experienced with the terms "limestone" and "sandstone," 

 but the meaning of the word "shale" is very indefinite. It seems best to assign 

 a compositional significance to these common terms. Under this scheme many 

 field determinations are subject to modification. For example, the Rochester 

 "shale" at Rochester is an argillaceous dolomite ; the Camillus "shale" is a 

 waterlime. The composition of forty New York sediments is shown by dia- 

 grams which emphasize the insufficiences of our present nomenclature. Ex- 

 amples are given where identification of formational units has been made by 

 microscopic means alone, these tests being confirmed by paleontological evi- 

 dence. 



The microscope focuses our attention on the dual character of sediments — 

 the cement and the mineral substances held together by the cement. A nomen- 

 clature is suggested which would be indicative of the dual nature of the com- 

 position of sedimentary rocks as revealed by the petrographic microscope. 



Read from manuscript. 



LIFE ERAS BEFORE THE CAMBRIAN 

 BY CHARLES R. KEYES 



(Abstract) 



Recent astonishing lowering of the life record into the abyss of time, as at 

 Steep Rock Lake, in Ontario, and in the Canadian and Montana Rockies, does 



