1855.] on Trains of Erratic Blocks in Massachusetts. 89 



and on the other, when most metamorphic, into a crystalline rock, 

 in which sometimes chlorite, sometimes hornblende and felspar are 

 developed. A large proportion of the green fragments, in trains 5 

 and 6, have evidently come from the ridge A, and a large propor- 

 tion of the whole from its highest summit d, upon which fragments 

 often 30 feet in length may now be seen, some of them having 

 probably constituted for years the exposed crest of the ridge, and 

 having in that position acquired a smoothed and rounded outline so 

 characteristic of the protuberances of hard rock in regions where 

 erratics and glacial striae abound. Such dome-shaped masses 

 are called " roches moutonnees," on the borders of Swiss glaciers. 

 Several of the fragments having this shape, and lying on the crest 

 of A, have been slightly removed from their original position, as if 

 just ready to set out on their travels. They are angular in their 

 lower parts, where they exhibit such an outline as the jointed rock 

 would possess if a great fragment fell from an undermined cliff. 



To the westward of the ridge A no similar green blocks are to 

 be found, not even a small number, such as we might have expected 

 to roll down to the base of a hill having so steep a western decli- 

 vity. It is evident, therefore, that the propelling power, whatever 

 it was, acted exclusively in a south-easterly direction. 



Dr. Reid has traced the train No. 5 for more than ten, and 

 No. 6 for more than twenty miles to the south-east, crossing the 

 Richmond and Lenox mountains B and C, and probably extending 

 beyond the points to which they have already been followed. Messrs. 

 Hall and Lyell found both trains extremely well-defined after they 

 emerge from the Richmond range, but by no means so distinct in 

 their passage over the first valley between A and B. A great 

 number of blocks have collected at the base of d, Fig. 1, or the 

 highest knob before alluded to of A, particularly around ^, or 

 Sherman's House. From this point to the Richmond range, a 

 nearly continuous stream may be traced, and the blocks are seen to 

 pass through a gap or depression, in the eastern division of the 

 ridge B, between Flat Rock and Merriman's Mount, k and /. But 

 when we attempt to follow the other train. No. 5, from its supposed 

 point of origin e, (a spot about half a mile distant from d before 

 alluded to,) we find at /an hiatus, not less than 175 yards long, 

 where there are no erratics. This break is not caused by the stones 

 having been used up for building, no such materials being obser- 

 vable in the walls enclosing fields, or in the farm-houses in the 

 neighbourhood. A vast number of blocks seem to have crossed the 

 valley in a direct line between A and B, and to have accumulated 

 on the north-western slope of Merriman's Mount /, as well as to 

 the south of it, around Dupey's Mount m ; and they seem to have 

 crossed the Richmond ridge by depressions both to the north and 

 south of Dupey's Mount, those to the north proceeding westward 

 to join the train No. 6. The number of large blocks lying on the 

 west slope of Dupey's Mount, and many of them to the south of 



