CONSTRUCTION OF THE OLEAN ROCK SECTION 



BY JOHN M. CLARKE 



The differing interpretations of the Olean section given by 

 Professor Glenn and Mr Butts in the papers preceding, afford an 

 excellent illustration of the discrepancy which often results 

 from the two modes employed. This discrepancy pertains how- 

 ever solely to the determination of a conventional boundary plane 

 in sediments characterized by the uniformity of their succession. 

 The sequence of events involves the independent construction 

 of the lithologic or purely stratigraphic evidence and of the facts 

 derived from the succession of faunas. In a great thickness of 

 arenaceous sediments carrying variable intermixture of clay, 

 slight and oft recurring differences of texture are produced and 

 these variations are so locally related to coastal contour and 

 bathymetry, to tidal ebb and flow and to stream discharge, that 

 sedimentary differences seldom hold true far away from a given 

 section. In the Upper Devonic of New York this marine arenace- 

 ous sedimentation prevails through a thickness of 2500 to 3000 

 feet. It has long been a subject of close study. By the con- 

 struction of a large number of meridional sections from east to 

 west through the lower or Portage division of this sedimenta- 

 tion we believe that we have now arrived at an understanding 

 of the proper correlation of sections which, in the actual suc- 

 cession of sediments, differ fundamentally. Doubtless with the 

 similarly close analysis of the Chemung beds we shall arrive at 

 an equally clear understanding of the succession and lateral 

 extension of sedimentary differences. If we have gained any 

 lesson from the careful analysis of these earlier or Portage sedi- 

 ments and their contents it is this, that in these shallow water 

 deposits there is very little correspondence between the sedi- 

 ments and the organisms that lived on them, that indubitably 

 continuous sediments may carry, without necessary variation of 

 texture, wholly different organic combinations at different 

 places; that faunas shift, encroach on the provinces of others 

 and retreat without concomitant change in the sedimentation. 

 Hence a history of the events of sedimentation from which may 

 be drawn the record of coastal alterations, of shifting coast lines 

 and bars, and, in consequence of increased or lessened terrestrial 



