76 rRGCEEDINGS OF THE CHICAGO MEETING 



the continuity of the glaciated surfaces from other places being reported, but 

 these have all been matters of a few inches. The escarpments about Mount 

 Toby have been discussed before this Society^ and their cause attributed to 

 plucking by the glaciated ice. It is almost a tradition that New England does 

 not offer recent diastrophic movements. 



Two years ago, needing a much more accurate map of the Mount Toby group 

 than any which have been made to date, I set my geology class to mapping the 

 region, both topographically and geologically, and the accompanying map, fig- 

 ure 1, is the result. One feature came out from the first. The shoreline of the 

 postglacial Lake Hadley was not where it was supposed to be. Shortly after 

 the glacial ice had disappeared Mount Toby was surrounded on the south, 

 west, north, and part of the east by this considerable sheet of water, and the 

 streams from the mountain brought into the lake quantities of gravel and 

 sand which were deposited in a very pretty series of deltas at the mouth of 

 each valley. The largest of the deltas is that of the Long Meadow Brook (a 

 in figure 1), around the southeast and south end of the mountain, a delta ex- 

 tending two miles or more along the base of the mountain and with a width 

 of a mile or more in places. Today it stands almost perfect, except for a small 

 notch, where, since the draining of the lake, the brook, after crossing the delta 

 top, has cut a small piece out of the margin. This notch is unusually small 

 because the brook, except in highest water, sinks into the gravel of the delta, 

 disappearing until it reaches the margin of this big deposit. The level fields 

 on the top of this delta stand at 340 feet above sealevel, conforming with the 

 level of the shoreline along the east side of the valley hereabouts. 



Traveling from this delta along the west side of Toby, the next delta is that 

 of Dug Brook (b in figure 1), a small stream which has built a delta of some 

 fifteen acres on the top ; but this level delta top stands but 260 feet above sea- 

 level. From here northerly — in fact, from / to c in figure 1 — the shoreline is 

 perfectly developed as a sandy bench from 25 to oOO feet wide on top. This 

 continues up to a marked escarpment {x-ij in figure 1), the whole distance 

 from the Long Meadow delta to the escarpment being about three miles. Be- 

 yond the escarpment the shore is traced by a series of small deltas and a less 

 perfect shore bench, but is along the 340-foot level again. 



The escarpment which cuts the shoreline is a clean-cut fault, or rather a 

 double fault, for the descent from the upper to the lower level is made in two 

 steps — the first of 50 feet, the second of 30 feet. This fault, when first encovin- 

 tered cutting the shoreline, trends north 10 degrees west for a quarter of a 

 mile out into the old lake bottom ; then it makes an abrupt turn to north 45 

 degrees east and continues a mile and more, gradually getting lower and 

 finally disappearing. This fault cuts the course of two brooks, and each tum- 

 bles over the escarpments in two waterfalls. At the edge of each fall the 

 margin of the escarpment is scarcely notched, showing that these brooks, 

 though in spring they carry heavy burdens of sand, have not yet had time to 

 wear down the edge to a material extent. This fault must, then, be of later 

 age than the period of the postglacial Lake Hadley, which was emptied by the 

 postglacial uplift of New England, the amount of uplift for this region being, 



- B. K. Emerson: The cirques and rock-cnt terraces of Mount Tobj-. Bull. Geol. Soc. 

 Am., vol. 22, 1911, p. 681. 



