TITLES AND ABSTRACTS OF PAPERS 161 



displacements in the superjacent Devonian strata as indicative of its repetition 

 or persistence later. An attempt is made to show the probable presence of 

 more of these overthrusts eastward in the metamorphic belt of western New 

 England, which would seriously affect some of the current correlations. 



Presented in abstract extemporaneously. 



Discussion 



Prof. B. K. Emeksoin : Very similar overthrusts of Cambrian and pre-Cam- 

 brian cover the IStockbridge limestone (Ordovician) along a north-south line, 

 running across the State on a line west of Pittsheld-Williamstown. Vertical 

 north-south faults appear in the limestones underlying this overthrust, and in 

 Dalton a series of shallow artesian wells has supplied the pure water that has 

 made the paper mills there so successful. The weight of the overthrust beds 

 has not been thought adequate to explain so extensive vertical faulting in 

 Massachusetts. 



Prof. W. J. Miller : I believe Professor Ohadwick has given a very suggestive 

 explanation of the causes of the extensive normal faulting of the eastern 

 Adirondacks. So far as I know, after some years of field-work in that region, 

 the main facts regarding the faults mostly harmonize with the hypothesis 

 offered. There is considerable evidence, however, that much of the faulting, 

 or at least renewed faulting along old fracture lines, has taken place since the 

 great overthrusting from the east and even since the removal of the overthrust 

 mass by erosion, and it is not clear to me how this relatively recent faulting 

 is to be accounted for by Professor Ohadwick's hypothesis. 



Reply was made by the author. 



EVIDENCE IN THE HELENA-YELLOWSTONE PARK REGION, MONTANA, OF 

 THE GREAT JURASSIC EROSION SURFACE 



BY D, DALE CONDIT 



(Al)stract) 



A wide-spread baseleveling over most of the Rocky Mountain region pre- 

 ceded the deposition of Jurassic sediments. Evidence of this in the Helena- 

 Yellowstone Park region is presented. From the Idaho State line northward 

 to the vicinity of Helena this erosion surface truncates beds ranging in age 

 from Triassic to carboniferous (Quadrant formation), some 1,000 feet lower 

 stratigraphically. 



Presented in abstract extemporaneously. 



"GIANT RIPPLES" AS INDICATORS OF PALEOGEOGRAPHY 

 BY WALTER H. BUCHER^ 



{Al)Stract) 



Objections are presented to the current interpretation of the "giant ripples" 

 in the Ordovician as wave-formed (oscillation) ripples. Their formation by 



Introduced by N. M. Fennemau. 



