REPORT OF THE DIRECTOR I919 4I 



extensive accumulations of such sediments on the south slopes of 

 the continuations of the Finger Lakes valleys and, specifically once 

 more, over the wide valley-flat south and west of Tully village. 



Wliile the correspondence in occurrence in both regions is suf- 

 ficiently exact to be indicative of the typicalness of the succession, 

 and in so far is suggestive, the two areas nevertheless differ in a num- 

 ber of respects. The Tully area has features that are lacking in the 

 Alpine map and others that are much more characteristically 

 developed than in the European region. The Tully area would 

 therefore warrant separate discussion if only because of these dif- 

 ferences. In pointing out such correspondence as exists there has 

 been anticipated a general statement of the origin of these glacial 

 series and, as such an explanation will be essential to a competent 

 appreciation of the individual phenomena to be found in the Tully 

 section, it follows next. 



Development of the Tully Glacial Series 



When the first advance of the glacial ice reached the Tully region 

 it encountered a considerable topographic barrier, the northern 

 escarpment of the Appalachian plateau, here foniied by the out- 

 crops, in an east and west belt, of the resistant Onondaga and Tully 

 limestone formations. These are both massive rock layers in con- 

 trast with the soft shales which lie under each of them. Because 

 of the greater resistance such massiveness gave these limestone 

 layers when under attack by the agencies of weathering, frost and 

 solution, they had broken down much more slowly than the shale 

 materials ; hence a cliff topography developed at the outcropping 

 edges of the limestone layers. Such is the history of weathering 

 escarpments generally and the Onondaga-Tully escarpment is no 

 exception to this. Once these more resistant layers had been broken 

 down over a given area, the soft shales beneath them crumbled 

 rapidly and their fragments were borne away by the streams. Im- 

 mediately to the north of the line where the limestones still 

 exist a broad lowland was therefore formed, the Lake Plains ; while 

 to the south of this line the country, still capped and protected by 

 these more durable rocks and also by the resistant Portage sand- 

 stones, kept a higher level and made the beginning of the upland 

 areas which in their larger aspect are called the Appalachian 

 plateau. The difference in elevation so caused is of considerable 

 magnitude and well defined, and it may therefore be well termed a 

 barrier to an ice mass moving down from the north. Thus the 

 actual rise from Syracuse to Tully, going up over the edge of the 



