CHAPTERXX. 



THE CHAMPLAIN PERIOD (Continued). 



THE CHAMPLAIN CLAYS. 



INTRODUCTION. 



On the retreat of tlie ice and on tlu- occupaiu'v of the basin h\ tlie 

 flood waters clays began to l)e deposited over all the bottom, far from the 

 shores, where the current was not too strong, and sands and gravels accumu- 

 lated off the mouths of all the tributaries, and were moved along the shore 

 lines by the shore currents and out into the dee})er water by the undertow. 

 The two deposits are therefore strictly contemporaneous, and their lamin;x? 

 are intercalated with each other at their point of junction (see p. G90). The 

 sands were pushed in deltas rapidly out over the clays, so that their jjlace 

 of junction is a plane with small shoreward dip. It is strictly synchronous 

 with this earlier jjortion of the flood sands, since, as detailed in tlie last 

 section, the increased velocity of the flood earned sands out over the clays 

 in every portion of the lake bottoms, even in the most sheltered, like the 

 East Street basin in Amherst. 



The scanty outci'ops of the clay, mostly along river gorges, are marked 

 by a line of purple dots (1 b c, PI. XXXV), this color having thus a litho- 

 logical value, while the other post-Tertiary colors on the map have rather 

 an orogra})hic value. 



The great importance and magnitude of this terrane can be seen best 

 in vertical sections, as upon the map it is represented only by thin lines 

 along the river courses and road cuttings and on the steep slopes of ter- 

 races; elsewhere it is covered by the succeeding beds of sand. 



CLAYS IN THE MONTAGUE LAKE. 



The clays appear in great force above and below Northfield village, 

 where the brooks cut back in the lake-bottom beds, and here they rise 233 

 feet above sea level. Southward they appear frequently in brook cut- 

 tings in the bottom beds, and at Northfield Farms they rise to 270 feet 



•i97 



