THE CONTINENTAL ICE SHEET. 385 



ously supposed. A good instance of this will be found in the description of 

 the strije on and near Mount Monadnock, in New Hampshire, by G. A. 

 Wheelock,* who says that he spent "many days during three j-ears" in 

 studying that region. His conclusions he thus sums up : " Do not these 

 irregular striae indicate a changeable and edd\'ing current inconsistent with 

 the motion of a glacier ? " 



Geologists have sought to overcome some of the difficulties presented by 

 the striation in Northeastern America^ by attributing to the continental ice 

 sheet the faculty of moving in two or more directions at the same time. 

 Thus Mr. Carll, one of the Assistants on the Second Pennsylvania Survey, 

 intimates his belief that the same contluent mass of ice ma}' flow " in differ- 

 ent currents, at various horizons, with unequal velocities, and in divergent 

 lines, dependent on circumstances controlling its movement." t Professor 

 Dana also accounts for the fact that a portion of the striation conforms to the 

 topography, while another part appears to be independent of it, by giving to 

 the mass of ice the power of flowing in various directions at the same time. 

 According to this view, while the lower portion of the ice mass was moving 

 in the valleys towards different points — as, for instance, in the Hudson and 

 Connecticut valleys, to the south, and in that of the Androscoggin to the 

 east — the upper portion, over the whole country, was making its way in a 

 general southeasterly direction, carried thither by the force of gravity, the 

 slope between the region north of the St. Lawrence and the Atlantic coast 

 being deemed sufficient to give the necessary motive force. The difficulty 

 of the problem will be better appreciated after thus learning the extraordi- 

 nary nature of some of the theories which have been originated in endeavor- 

 ing to solve it. 



That the continental ice sheet has been extended far beyond the limits 

 which ought by any possibility to be claimed for it is, as the writer believes, 

 perfectly evident. This has happened because inexperienced observers, 

 having adopted the theory that all the drift phenomena are the work of a 

 continental glacier, have covered every region with ice Avhere any rolled 

 detrital materials of northern ori2;in could be found. Thus we often find the 

 southern limits of the ice sheet of Northeastern America drawn so as to in- 

 clude a large part of Indiana, Illinois, Iowa, and Minnesota, while there is 

 abundant evidence pointing clearly to the fact of its never having had any- 

 thing like that extension to the south. 



* American Naturalist, Vol. VII., 1873, pp. 466-470. 

 t J. F. Carll in Second Pennsylvania Report, III. p. 380. 



