HISTORY OF DERRYFIELD. 3I 



basins they afterwards occupied. It is true that they no longer 

 occupy anything that resembles a basin, but lie high above the 

 present water-level. But before the bed of the Merrimack be- 

 came continuous and finally sank to the level of our time, the 

 rock-barriers at Garvin's, Hooksett, Amoskeag and Goffe's falls 

 must have given way, at least sufficiently to drain the lake. The 

 first business of the released water would be to carve a channel 

 through materials of the least resistance, and prodigious quanti- 

 ties of clay went out, possibly to form new deposits elsewhere, 

 leaving the remainder of the beds where they are found to-day. 



It is not easy to conceive of the origin of such vast accumula- 

 tions. We know that the chief ingredient of the finer clays is 

 decomposed felspar — pure kaolin — and we are at no loss to 

 locate this mineral in the almost universal presence of felspathic 

 rocks in this region, notably granite and gneiss. These rocks, 

 then, supplied the materials, and the very fact that it was yield- 

 ed in such enormous quantities is an independent witness to the 

 magnitude of those sub-glacial phenomena to which so many of 

 the common facts of to-day are to be referred. The former 

 presence of felspar in excessive quantities in this locality is evi- 

 denced by the composition of the rocks in certain abandoned 

 quarries, notably along the Hooksett road, where may now be 

 found remarkably fine crystals of felspar of unusual size. 



As to the precise method by which the clays as we know them 

 were in the first instance formed there is scant evidence, and 

 the subject asks for further treatment at the hands of geological 

 experts. Authorities assert, however, that the stones in the 

 ever moving and shifting ice were ground together and that the 

 fine dust thus liberated was transported by water to suitable 

 points of deposit, resulting in beds of clay or earth. 



It may further be borne in mind that during and immediately 

 following the final melting of the ice-cap much of the accumu- 

 lated earth, clay, gravel and stones were left in unstratified de- 

 posits, in immense quantities and often of great height, and that 



