1S76.J 49 [Wright. 



making them 91 feet above the base assumed at 0, and 132 feet 

 above the river. Branches not adequately indicated on the map run 

 off at various points and form enclosed basins, which have no outlet 

 except as channels have been cut through the loose material of the 

 ridges, either by natural or artificial means. 



Quite an extensive body of water was included, till long after the 

 settlement of the town, in an enclosure between b and c. It has been 

 drained, partly by a channel of its own formation, and partly by arti- 

 ficial means, and is now occupied by a muck swamp, which is 20 or 30 

 feet deep. A trigonometrical section of the West Ridge, at the point 

 c, gives the height above the swamp at its base 61 feet, with a thick- 

 ness of 250 feet. The slant is 30°. The river bottom from which we 

 started is 50 feet above the ocean, so the extreme height of the West 

 Ridge at the point of measurement is 182 feet. A few rods east of 

 the point o there are irregular remnants of ridges of the same gen- 

 eral character with the others, running southeast to the Shaw shin, 

 and east of the Shawshin there is a continuation with little interrup- 

 tion to the point x, where it is apparently pushed into a great num- 

 ber of irregular prominences enclosing numerous bowl-shaped basins; 

 one of which, of oblong shape and about fifteen feet deep, is at the 

 very summit, the rim of which rises to a height of about 100 feet 

 above the river. The base of this part of the formation is on a level 

 with the Shawshin, and hence about forty feet lower than those for 

 which the measurements have been given upon the other side of the 

 small river, the substratum of rock being that much higher in the 

 one place than in the other. 



A mile south, at Pomp's Pond, on the eastern side of the Shawshin 

 valley, and partially connected by- intervening ridges, is a similar 

 cluster of rounded hills and enclosed basins, surmounted by a sharp 

 peak of still greater height. 



We should also observe, that clusters, or ganglions, of such irreg- 

 ular ridges, encircling bowl-like reservoirs, and rising into sharp 

 peaks, occur at frequent intervals along the whole belt of the forma- 

 tion we are describing. Frequently, as a ridge is suddenly pushed up 

 into a pinnacle, it will put out a spur, returning to itself and forming 

 a closed basin at or near its top, as south of the point c on the map. 



Before paying further attention to the course of the series north 

 and south, I will describe its composition and structure. It is import- 

 ant to notice that the material in the ridges is not uniformly, nor 

 every where stratified. The ridges themselves are ordinarily com- 



PROCEEDINGS B. S. N. H. — VOL. XIX. 4 MAY 1877. 



