GLACIAL DRIFT. 1 97 



ogy of Massachusetts, and in his text-book. He says of it, — " From top 

 to bottom it has been scarified on its northern and western sides. On 

 its lower parts, especially on the south-west side, the striae run about N. 

 W. and S. E., by the magnetic needle, as they do in the country around 

 the mountain ; but, when we approach its top, the course changes to N. 

 io° W. and S. io° E. Other stride are seen here on steeper slopes, both 

 northern and southern, than I have found elsewhere." 



The observations given in the table were mostly taken in 1871. It 

 would appear that the common direction in the vicinity of Monadnock 

 is about S. 12° E., the towns north showing a few degrees additional of 

 easting, while the mountain itself, from the lake to the south-west corner 

 of Jaffrey, about eight miles, exhibits, on its north-west flank and southern 

 edge, the south-east course. After looking over the whole area, one sees 

 that the ice coming from the north and west of north struck the moun- 

 tain and clung to it closely, so much so as to run much more easterly on 

 the south edge than elsewhere. Over the region to the south-east all 

 trace of this easting is lost, the striae in Jaffrey running S. 11° E., much 

 like those of Troy and Marlborough. I have not explored the east side 

 of the mountain ; it is mostly covered by trees. Hence it is impossible 

 to decide upon the value of Mr. Wheelock's theory, from present explora- 

 tions. I understand his view to be, that Monadnock was an island in a 

 sea full of icebergs, which struck equally strong upon both the north-west 

 and south-east sides. There is certainly a dearth of striated ledges upon 

 the south-east side, while even the earth has been largely removed from 

 the north-west flank, so mighty has been the planishment of the rock. 

 The striae on the south-east side should all point south-westerly, if the 

 summit were an island scarified on both sides by icebergs. Mr. Whee- 

 lock's paper is a very valuable one ; and that part which relates to striae 

 is herewith reproduced. 



StricB on Mt. Monadnock.* Having, in the last three years, spent many days in 

 studying the strias upon Mt. Monadnoclc, the writer is unwilling that the results of his 

 observations should be lost for want of record, especially as they seem to have an im- 

 portant bearing upon unsettled questions of surface geology. This mountain is pecul- 

 iarly favorable to such study. Its long spurs radiating from a central elevation, though 



* American Naturalist, vol. vii, 1873. 

 VOL. III. 26 



