Wright. 50 [December 20, 



posed of sand, gravel and pebbles, the latter from a few inches to two 

 feet through, sometimes irregularly stratified, the coarse material be- 

 ing as likely to abound near the top as at the bottom; at other times 

 10 or 15 feet or more in thickness will give no signs of stratification 

 whatever. The top of the ridge is usually just wide enough for a 

 foot path, and pebbles a foot or two in diameter dot its course at 

 frequent intervals. Usually, also, the base of the ridge is partially 

 hid by subsequent accumulation of stratified sand and fine gravel, or 

 by peat bogs. 



Another point of importance is, that the fragments of rock in the 

 ridges are nearly all somewhat rounded and apparently water worn, 

 though it is evident that they have not all been subjected to the 

 same amount of attrition. I have searched in vain among the de- 

 Ibris of the formation for scratched stones, though striated stones are 

 .found in abundance near the surface in the immediate vicinity. Fur- 

 thermore, the pebbles are not of local origin. I am not sufficiently 

 acquainted with the region to the north to determine the original 

 locality of all of them. Merrimack slate abounds, however, as does^ 

 a gneiss, with peculiar crystals of feldspar, whose " habitat " is well 

 determined in central New Hampshire. In Topsfield a portion of 

 the pebbles are clearly from ledges only a few miles to the northwest. 



Keeping these characteristics in mind, we will now note the extent 

 of the series so far as known. Between two and three years ago, 

 and in ignorance of what Mr. Upham of the New Hampshire Geo- 

 logical Survey was doing, I began to prosecute investigations to 

 determine more precisely the character and extent of the phenom- 

 ena described. It was soon found that the system extended indefi- 

 nitely along a line northwest by southeast, constituting a reticulated 

 belt of gravel ridges a half mile or more wide, nearly coincident in 

 general direction with the course of the striae on the rocks, and with 

 the line of prolongation of the axis of the Merrimack Valley from 

 Manchester upwards. 1 The formation does not lie at a uniform alti- 

 tude above the sea, but rises over hills and descends into river valleys 

 in a certain apparent independence of the natural configuration of 

 the country. The land, however, though undulating and somewhat 

 broken, nowhere in this part of Massachusetts rises more than 300 

 or 400 feet above tide water. The ridges plainly belong to the super- 

 ficial deposit, since they everywhere overlie the " boulder clay " or 



1 " Reticulated Ridges " is the happy descriptive phrase applied to the forma- 

 tion by Professor Shaler. 



