FULLER : NOTES ON A CARBONIFEROUS BOULDER TRAIN. 255 
the latter of 67°. The outcrop selected by Professor Crosby, being 
of very limited area, allowed not only the determination of the 
eastern boundary, but that of the western boundary as well. The 
bearing of the latter is approximately S 23° E. Assuming a similar 
rate of fanning for both trains, this would indicate the most south¬ 
erly movement of the ice passing over the ledges of red sandstone 
to be about S 16° E. In Hingham, as in Braintree and Weymouth, 
the boundary was found to be curved. The direction of the longer 
axes of the drumlins in the Hingham area corresponds roughly to 
the average direction of the ice movement; that is, about S 45° E. 
In marked contrast with the rapid fanning observed in both of 
the above trains, is the slow fanning noticed by Professor Shaler 
(’93, map) in the study of the train leading from Iron Hill at Cumber¬ 
land, R. I. In the Hingham train the width increases from a few 
hundred feet at the start to some 16,000 feet at a distance of four 
miles, while in the Iron Hill train nearly four times this distance is 
required to give a similar amount of fanning. The general direction 
of the Rhode Island train is about S 15° E near the point of origin, 
but becomes nearly due south on coming within the influence of the 
depression now occupied by Narragansett Bay. 
In still more marked contrast with the Braintree and Hingham 
trains is the once famous Richmond train of western Massachusetts 
mentioned and discussed by Reid, E. Hitchcock, II. B. Rogers, 
W. B. Rogers, Lyell (’55), Perry, and Benton, which affords an 
example of a train that not only shows, at least in the limits studied, 
no fanning,' but which shows an actual contraction in its width, 
decreasing from 430 feet at the start to 200 feet on Lenox Range 
(Benton, ’78). 
Cause of fanning. — Fanning, or the divergent distribution of 
material, may be brought about in a variety of ways. Of these, 
irregularities in the amount or in the distribution of the precipitation 
and the consequent irregularities in the velocities and directions of 
the ice movements are, perhaps, the most general. Following close 
upon these, in relative importance, are changes and irregularities in 
ablation both as the result of climatical changes and of the influence 
of debris in or upon the ice. Subglacial drainage may also, in 
cases, serve to carry material beyond the limits which the ice move¬ 
ments would have established for it. These causes, however, are 
all of a general nature, and, though indirectly of much importance, 
are not directly applicable to the fanning of the boulder trains of 
