52 H. L. FAIRCHILD — ICE EROSION THEORY A FALLACY 



ph y which has preserved not only evidences of ice work, but very satis- 

 factory proof of the slight amount of work. Doctor Gilbert has drawn 

 attention to the erosion phenomena in the short but interesting paper 

 already noticed and which we shall quote again. 



Against the Niagara escarpment the Ontarian ice body impinged in 

 the most effective way, both in momentum and direction. The move- 

 ment was oblique to the cliff; and every mechanic learns that his cutting 

 tool, chisel, rasp, or plane, does its best work when the cutting edge is 

 held oblique to the line of motion. During all the life of the Laurentian 

 ice in this localit)^ in all stages of its flow, the glacier struck this barrier 

 at the very best advantage; and with what effect? The cutting by the: 

 ice has been just about sufficient to prove that it was comparatively ver} 7 

 slight. More or less cutting might have left the record equivocal. 

 Doctor Gilbert has described (figure 2) how the ice cut oblique notches 

 in the crest of the escarpment. A horizontal profile along the brow of 



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i i i i iii 1 1 , i 1 1 1 1 1 1 • i Miles 



Figure 2. — Contour on the Lockport Limestone at the Niagara Escarpment. After Gilbert. 

 The escarpment faces north. Arrows show observed directions of glacial strise. 



the scarp is serrate, with the serrations directed to the northeast, or 

 against the ice-flow. Many, if not all, of these notches were originated 

 by preglacial agents, and the ice has rubbed them, sometimes enlarging 

 them and changing their axial direction. Doctor Gilbert says : 



"All the more general features of the limestone belt thus seem to be preglacial." 



After describing the limestone cliff in its form, relations, and erosion, 

 he concludes as follows : 



" The configuration of the cliff seems to show that in the regions where the trend 

 is southwest all minor salients have been pared away by the ice, and that where the 

 trend is southeast minor irregularities of the face have been exaggerated and small 

 reentrants drawn- into furrows; but the principal salients and reentrants of the 

 topography are preserved, and ice modification is limited to minor details of form. 



•' . . . It would appear that the ice sheet concentrated its work, so far as the 

 Niagara limestone is concerned, on the crest of the escarpment, and that even 

 there its results were of secondary rather than primary importance. Probably the 

 limestone at its escarpment lost on the average only 10 to 20 feet of thickness, and 

 from the broad belt of outcrop the general loss may have been as small as 5 feet." 



With the above descriptions and conclusions the writer is in accord, 

 and the estimate of removal on an average of 10 to 20 feet of rock from 



