220 J . \\\ SPENCEB POSTGLACIAL EARTH-MOVEMENTS 



accumulations of this eastern arm of Lake Iroquois. These have an ele- 

 vation of -±15 feet above sealevel at Ronie and ±06 feet at Herkimer and 

 at Mohawk, with remnants of the same gravel deposits at Little Falls., 

 which is nearly in the same latitude. These observations furnish data 

 for determining the earth-movements farther southeastward, showing 

 that this locality is beyond the axis of postglacial elevation, and tha: 

 the apparent warping here is downward. 



A higher terrace of the Mohawk is of great importance. East of Her- 

 kimer the front of this gravel deposit, resting on clay, rises some 90 to 

 110 feet above the Iroquois plane. A similar elevation of the terrace is 

 repeated some -1 miles north of Eome and elsewhere. This higher water 

 plane is older than that of Lake Iroquois, and requires further investiga- 

 tion, but it throws suggestions on the shorelines north of the Adiron- 

 dacks. 



Xorth of the Mohawk Valley other terraces occur at still higher eleva- 

 tions. Thus one of great magnitude may be seen northwest of Trenton 

 Falls, on the road to Prospect, at 260 feet above the broad valley, or be- 

 tween 1,010 and 1,030 feet above tide, with the plains at Prospect at 

 1,1 TO feet. These all face the south, showing open water in that direc- 

 tion; but only the lower terraces need to be mentioned here. 



Features oe the Country Xorth oe the Adirondack^ 



The ancient preglacial surface of the country, descending some 2,000 

 feet northward from the Adirondack plateau, was deeply dissected by 

 broad valleys, now covered with a mantle of drift, yet these have still a 

 depth of from 50 to 300 feet. In them terraces, deltas, and broad plains 

 of sand and gravel occur, both near the levels of the streams and at 

 higher elevations. Consequently all the old shorelines north of the Adi- 

 rondacks have been much interrupted by the former estuaries, so that the 

 observation must now be made, sometimes on the beach ridges or again 

 on the corresponding terraces or deltas. Generally there are no topo- 

 graphic maps of this region to give even imperfect assistance in follow- 

 ing the shorelines which rise from one contour to another. Such fea- 

 tures make the identification of a particular strand somewhat difficult, 

 unless continuously followed and the elevations determined by the spirit- 

 level. This method was used by me to a point 4 miles east of TTatertown, 

 while beyond the measurements were by aneroid. This instrument origi- 

 nally indicated that the beach near Stirling Bush was too low. which led 

 to the finding of the higher strands at Xatural Bridge and at Fine, 

 which are now seen to be above the Iroquois plane, while the measure- 

 ments of the corresponding ridge road at Pitcairn was excessive in height. 



