776 ABSTRACTS OF PAPERS 



to the minimum diameter of one-eightieth of an inch, materials below this size 

 being removed. The unusual roundness of these wave-worn sands he accounts 

 for through the cooperation of tidal and wave action holding them on the 

 shoal and subjecting them to continual wear. By the cooperation of waves 

 and currents he concludes that such wear may extend broadly to a depth of 

 as much as 40 fathoms. This raises the question as to the limit of fineness 

 and roundness of grains which might be attained on the bottom of an epicon- 

 tinental sea, everywhere shallow and to which sand was the dominant material 

 supplied. The conditions are quite different from the common cases of river 

 and beach action. 



Fourth, it is well known that along the flat sandy coasts of humid lands, 

 such as much of the Atlantic coast of the United States, wind action plays an 

 important part in moving and wearing the sands which have but recently 

 been transported by wave action, and much of these wind driven sands may 

 again become portions of marine deposits. To what extent, therefore, in a 

 slow and oscillating marine movement across baseleveled lands may eolian 

 action cooperate in shaping the grains of sand independently of the climate? 

 At the present time eolian action in deserts is an agency of first importance 

 and marine oscillations across sandy plains are at a minimum. In those 

 epochs, however, when the latter was a widespread and characteristic geologic 

 activity, is there not danger of a too hasty inference as to the existence of an 

 arid climate based upon evidence of eolian action in the wear of the sand 

 grains? 



For example, two decades before the British geologists began the study of 

 the significance of this subject Logan noted, in 1863, the rounded character of 

 the sand grains in the Potsdam sandstone, a formation which is regarded as a 

 typical example of a slow marine transgression of a baseleveled land. 



Consequently, in view of these queries, although valuable and suggestive as 

 the studies of ancient sand grains have shown themselves to be, there is, how- 

 ever, apparently need of more exhaustive study of modern sands accumulated 

 under determined conditions in order to apply that knowledge with greater 

 precision to the past. 



Prof. W. M. Davis : I wish to suggest that in collecting specimens of sand 

 it is desirable to indicate the distance of transportation during which the 

 sand has been under the action of the agency concerned; also that it would 

 be well to use a higher magnifying power, sufficient to show the texture of 

 fractured or frosted surfaces as well as the general form of the grains. 



Prof. A. C. Lane: Referring to Professor Barren's remarks, I •think it is 

 not so much a question of "transgression" as transportation along shore, like 

 the Florida deposit cited. Having had occasion, also, to study the Sylvania, 

 I am inclined to differ from Professor Sherzer somewhat in emphasis. I agree 

 with him that part of the Sylvania is waterlaid with its dolimitic cement; 

 that in places it is eolian, and that the climate was arid, but I am inclined to 

 lay more stress on derivation from a previously fairly concentrated quartz 

 sandstone by transportation along shore some distance as a factor in the 

 peculiar character of the Sylvania. 



