l895-] FAIRCHILD GEOLOGY OF THE PINNACLE HILLS, 177 



Structure and composition made the hills a puzzle to earlier students. 

 In 1892 the hills were observed by Mr. Warren Upham, who pub- 

 lished in 1893 in these Proceedings* a paper describing them as an 

 Esker, or gravel ridge, laid down in the ice-walled channel of a 

 glacial river. After detailed study of the deposits the present writer 

 finds an explanation of their genesis radically different from that 

 of Mr. Upham. 



The Pinnacle hills were not accumulated in the bed of an over- 

 loaded stream, flowing toward the ice front, but were piled along 

 the edge of the glacier. They are part of a frontal moraine and con- 

 sist of the debris washed out of the ice sheet by the drainage, along 

 with considerable unmodified drift deposited directly by the ice. 

 The hills are essentially morainal, but being chiefly waterlaid drift, 

 sand and gravel, are technically called Kame and may properly be 

 termed Kame-moraine. The various reasons for this interpretation 

 of their origin are briefly epitomized as follows : 



The hills are not a ridge but a belt of knolls; the range having a 

 curvilinear trend, with the convexity southward. The general direc- 

 tion of the chord of the arc is W. 15° S. The morainal deposit is 

 continued westward from the Genesee river as a low but distinct 

 moraine as far as Albion, which was first traced by Mr. Frank 

 Leverett. Other morainal phenomena occur eastward and beyond 

 the Irondequoit gulf. The topography of the range is emphatically 

 morainal, knob and basin, or mound and kettle. The stride upon the 

 underlying rock, Niagara limestone, are in two sets, the older having a 

 direction S. 40°-6o° W. and the later nearly at right angles to the 

 curving moraine. The northward face of the range is very steep 

 and irregular, the deposit upon that side having been banked against 

 the ice and left at the angle of repose by the removal of the ice 

 support. The southern slope is usually gentle and uniform. This 

 difference is seen clearly by looking eastward to Cobb's hill from the 

 "Pinnacle." The presence of much till in the range, especially upon 

 the north slope and summits, is significant. Heavy boulders occur 

 upon the very crest of the ' ' Pinnacle, ' ' and the southern ridge of Cobb' s 

 hill is a mass of remarkably heavy boulder till. The disturbed, 

 crumpled and crushed condition of the beds along the north slope 

 indicates a pushing or overriding by readvance of the ice front. The 

 beds along the north side dip steeply southward into the range, and 



•Vol. 2, pages 181-200, February, 1893. 



