THE TILL. 533 



By far the finest development of river pot-holes is in the almost inac- 

 cessible canyon of the sonth branch of Westfield River, one of which is 

 25 feet deep and 20 by 10 feet at the mouth. They exist abundantly 

 along- the course of Deerfield River, in many cases high above the present 

 level of the river, as noted by President Hitchcock. I counted more than 

 50 on a single reef of sandstone which projects into Deei-field River at the 

 most northerly point reached by the stream before it turns toward its 

 notch in the trap range. One is found by tlie road to the south side of 

 Catamount Hill, in Colerain, 2 feet deep and l^ feet wide. 



The only pot-hole, however, which I can without hesitation assign to tlie 

 Glacial period I found l)y the roadside under the steep southern face of 

 Sug-ar Loaf, in South Deerfield. It is in red sandstone at a point 130 feet 

 above sea, and is 2 feet deep and 2 feet wide. From its position it must 

 have been fonned during some phase of the Glacial period, as it lies apart 

 from any probable stream bed, and the surfiice of the sandstone around it 

 is striated. I have surmised that these usual accompaniments of glacial 

 action, which we .should especially expect to find in so irregular a region, 

 may have been many times formed and again eroded and destroyed by the 

 ice, and that this may be the origin of many of the spherical, ovoid, and 

 flat-ellipsoidal pebbles of quartz which occur here in considerable numbers 

 in the true till and which agree quite exactly in form with the polishing- 

 stones of a pot-hole. However, they may belong- to a coarse-pebble beach 

 of inter-Glacial age, synchronous with the pink sands described below. 



THE TIT.L,. 



INTRODUCTION. 



Pure ice moving over the coiintrv would bv its tlu-ust tear off project- 

 ing portions of the subjacent ledges, but could not alone polish and scratch 

 the rocks as we find them now. The agents of this work were the stones 

 themselves, which, torn from their places and frozen in the ice, trans- 

 formed it into an immense I'asp and increased its eroding power many fold 

 By the melting and freezing of the lower surface and by the slow intestinal 

 motion, as well as by the sudden fissuring of the mass, its lower portion 

 would become filled with a large and varying quantity of loose, rocky 

 material. 



Also, where, by secular decomposition, as indicated on page 374, the 

 rocks had become softened to great depth, the whole, soaked with water, 



