THE CIIAMPLAIN PERIOD. 063 



We have first to discuss lakes at elevations of 800 to 1,000 feet above 

 sea, liekl back in basins on the eastei'n border of the region, high up on the 

 western slope of the great plateau of central Massachusetts, whicli were set 

 free by the first melting of the ice over the area. We must then studv 

 how the continued retreat of the ice uncovered gradually a more and more 

 complex network of longitudinal and transverse valleys in which successive 

 series of lakes and rivers found temporary place and were drained f)ver 

 passes now abandoned, as these passes were one after the other, and at 

 lower and lower levels, opened by the ice. We shall see how this melting 

 process went on until at last the space between the eastern rocky Ijorder 

 slope of the main valley and the tongue of ice still extending southward 

 in the valley from the main mass became a channel liy which for a time 

 the waters escaped into the open valley below, and in which they lodged 

 a great mass of coarse, tumultuously irregular, kame-like sands. These 

 sands were afterwards in greater or less measure planed down to the level 

 of the high terrace formed by the flood waters which occupied the Con- 

 necticut Valle}', and as they often covered masses of the retreating ice, are 

 now deeply pitted here and there at the surface by kettle-holes, or have 

 sunk down into a system of reticulate ridges, due to the melting of the ice. 



\Vliile the bottom of the valley on a given latitude was still covered 

 by the ice and kept free from the deposits of the melting, it is everywhere 

 indicated, for the central portion of the vallev at least, that the tongue of 

 ice was thrust at its southern end into deep water, buoyed up and floated 

 ofl", and was immediately succeeded by the laminated clays. All along 

 the western border a complex and interesting series of beds show clearly 

 the alternate advance and retreat of the ice, at least three times repeated, 

 and the high terrace on this side is comparatively narrow, and in many 

 places remote from the mouths of streams is represented only by a narrow 

 shelf in the rock or by a notch in the heavy deposits of till. The high 

 terrace is not, as is often the case on the eastern side, represented by a 

 broad area of kame-like sand which is planed down to its level, but is of 

 earlier date of deposition than the time of the highest level of the flooded 

 Connecticut. On both sides the high terrace or l)encli which marks the 

 highest stage of the Connecticut lakes may be defined as a series of deltas, 

 but those on the west are proportionately much less extended and of finer 

 material than those on the east. Moreover, in the northwest corner of the 



