1855.] on Trains of Erratic Blocks at Massachusetts. 93 



island of the same group, might float on till it reached the clianuel 

 between B and C. Year after year two such exposed cliffs in tlie 

 Canaan range as c?and e (Fig. 1), undermined ])y the waves, might 

 serve as the points of departure of blocks, composing the trains 

 Nos. 5 and 6. It may be objected that oceanic currents could not 

 always have had the same direction ; this may be true, but during 

 a short season of the year when the ice was breaking up the pre- 

 vailing current may have always run S.E. 



If it be asked why the blocks of each train are not more scattered, 

 especially when far from their source, it may be observed, that after 

 passing through sounds separating islands, they issued again from a 

 new and narrow starting point ; moreover, we must not exaggerate 

 the regularity of the trains, as their width is sometimes twice as 

 great in one place as in another ; and No. 6 sends off a branch at 

 p, which joins No. 5. There are also stragglers, or large blocks, 

 here and there in the spaces between the two trains. As to the dis- 

 tance to which any given block would be carried, that must have 

 depended on a variety of circumstances ; such as the strength of the 

 current, the direction of the wind, the weight of the block, or the 

 quantity and draught of the ice attached to it. The smaller frag- 

 ments would, on the whole, have the best chance of going farthest ; 

 because, in the first place, they were more numerous, and then being 

 lighter, they required less ice to float them, and would not ground 

 so readily on shoals, or if stranded, would be more easily started 

 again on their travels. Many of the blocks, which at first sight 

 seem to consist of single masses, are found, when examined, to be 

 made up of two, three, or more pieces, divided by natural joints. 

 In case of a second removal by ice, one or* more portions would 

 become detached and be drifted to different points further on. 

 Whenever this happened the original size would be lessened, and 

 the angularity of the block previously worn by the breakers would 

 be restored, and this tendency to split may explain why some of the 

 far-transported fragments remain so angular. 



In the ravine between Merriman's Mount and Flat Rock {k and /, 

 Fig. 1), the erratics, instead of following a N.W. and S.E. course, 

 run within 10 or 15 degrees west and east; and Messrs. Hall and 

 Lyell observed that the glacial furrows there on the exposed rocks 

 below deviated in like manner from the normal direction, and were 

 directed like the train of erratics nearly west and east. They were 

 told that the like deflection, both of trains and furrows, was observ- 

 able where Nos. 5 and 6 cross the Lenox range ; and this deflection 

 is so represented on the plan (Fig. 1); although the speaker had 

 not an opportunity of verifying the fact. The direction of floating 

 ice, when threading the sounds separating islands, would be governed 

 by the shape of the land and the marine channels, and might be 

 expected to differ from the direction of currents flowing in the 

 open sea between chains of islands. 



Sir C. Lyell endeavoured in 1842, when explaining the origin of 



