ALGONKIAN ROCKS IN VERMONT. 397 



square miles. This area has a maximum width on the south of 

 ten miles and a minimum width on the north of four miles. The 

 delimitation of the Pre-Cambrian as just given is only approxi- 

 mate, as in many localities data for its separation from overlying 

 rocks are lacking. 



TOPOGRAPHY. 



The Geological Survey has lately issued topographic maps 

 of nearly all the territory embraced in the above-outlined area ; 

 in them the pronounced relief of the country is well shown. 

 These maps are the Rutland and Wallingford sheets. An 

 inspection of the topography reveals a line of high elevations on 

 the west, with steep slopes to the east, and steeper slopes com- 

 monly on the western side. This line of mountains extends from 

 the southern limit of the Wallingford sheet to the northern limit 

 of the Rutland sheet, and is only broken by narrow transverse 

 valleys where lateral streams come in from the east or southeast 

 and join Otter creek in the Rutland valley. On the east side 

 of the area a similar range of high mountains extends the same 

 distance, but coalesces with the western line in the northern part 

 of the Rutland sheet. The convergence of the two lines is geo- 

 logically dependent on a narrowing of the series of folds, which 

 originally mantled over the central part of the area. North of 

 Ludlow mountains an offset to the east occurs which carries £he 

 line slightly to the east of the Wallingford sheet. 



It will be noticed on the, Wallingford sheet that there is a 

 central area between the border line of mountains of relatively 

 much lower elevations. From Copperas hill in Shrewsbury one 

 observes that the mountains appear to encircle him with a line of 

 much higher elevations. In a country of strong relief one is 

 always impressed with a sense of being in the centre of a series of 

 elevations of greater height than those in the immediate vicinity. 

 But from Copperas hill the impression is borne out by a glance 

 at the topographic maps. On the east and west are the two lines 

 of mountains just described ; to the south, but farther away, the 

 country begins to rise towards the high peaks of Stratton and 

 Somerset ; to the north, just north of the town of Shrewsbury 



