220 SURFACE GEOLOGY, 



commenced to change. Two tributary valleys from the north, Mill and 

 Whittier brooks, may show striation coursing more southerly ; but these, 

 and all the rest of the Smith's brook region, have not been specially 

 examined with the object of noting the glaciation. The lower part of 

 Smith's river changes its course so much that if a mass of ice followed it, 

 the variation in the direction of the striae would be very observable. 

 Between Alexandria and Hill there has been considerable excavation 

 since the ice period, so that the markings may be looked for away from 

 the stream. We have good reason to expect to find evidence of local 

 action all along Smith's river, provided the ledges are not too much cov- 

 ered up. 



Blackzvatcr Valley. The map of local glaciers in Volume i represents 

 the movement of the ice as continuous from Grafton and Danbury along 

 the railroad, to connect with that in Andover along the Blackwater. I 

 have separated them now, because it seems more natural for the ice to 

 flow down Smith's river to join the Pemigewasset, than to cross the Dan- 

 bury water-shed, where the necessary rise is not far from a hundred feet. 

 The course in the south part of Grafton, on the highlands, is such that 

 the continental sheet points directly to Andover, or to the valley between 

 Mts. Ragged and Kearsarge. It is not therefore certain that the ice go- 

 ing down the Blackwater, whose marks remain, should be classed with 

 the later movements. But it is certain that the course was modified by 

 the valley, so that it belongs to the category of those motions whose 

 course did not proceed in defiance of elevations and depressions of the 

 surface. Several ledges at Potter Place and Andover show that the 

 course was much more easterly than the very east directions upon Kear- 

 sarge and Ragged [see page 200]. It has 20° more easting than on 

 Kearsarge, and 40° more than upon Ragged. This course would natu- 

 rally turn at Andover Centre, and proceed southerly through Salisbury, 

 if it continues to conform to the valley, and not climb the hill at East 

 Andover like the railroad. Such facts as are reported confirm this view. 

 The East Andover ridge is occupied by drift, perhaps lenticular mo- 

 raines ; and the striae in West PVanklin run S. 32° E., and therefore 

 belong to a different movement. The top of a hill west of the Black- 

 water, on the south town line, shows the course S. 38° E., and on its 

 south slope arc stria; running down hill towards Salisbury. And in this 



