198 BULLETIN OF THE 
movement of the rocks from the central path of the train is about one 
tenth of the direct forward movement. 
At the source of the train the peridotite boulders are plentifully in- 
termingled with, and to a certain extent overlaid by, materials brought 
from the region which lies to the northward of Iron Hill. It is evident 
that these schistose rocks yielded an abundance of erratics,-and it is 
therefore not surprising to find that even at the outset the train has 
not more than one tenth of its mass made up of the fragments of ore. 
The remarkable fact is that the boulders of peridotite rather plentifully 
occur on the surface of the drift in the section immediately to the 
south of the place whence they were derived. This thorough com- 
mingling of the débris from different. parts of the erosion field clearly 
indicates that there was some feature of movement in the ice which 
tended to comingle the detritus which it bore, and to effect the com- 
bination in a very rapid manner. In other words, the vertical scatter- 
ing of the fragments in the body of the glacier evidently went on 
simultaneously with the horizontal dispersion which brought about the 
widening of the belt over which they were dispersed. At the distance 
of not more than half a mile from the source of supply the intermixture 
of the peridotite boulders with those derived from the bed rock appears 
to be complete. The occasional artificial sections in road cuttings and 
wells show this feature in a clear manner. 
It should be noted that the average distance between the pebbles of 
ore rapidly increases as we depart from the source of the train, and that 
this increase is accompanied by a somewhat proportionate diminution 
in the size of the fragments. This is approximately represented in the 
following table, which assembles the observations made on many thou- 
sand erratics in the section of the train between Iron Hill and Provi- 
dence. South of that point, as before remarked, the greater part of 
the trail is covered by the waters of Narragansett Bay. 
Place. Average Diameter. Largest Fragments observed. 
At source. 3 feet. 5 feet. 
2 miles south. 2) <SGiin: as 
4 “ ce 1 “ 6 “ 8 «cc 
6) ssé 5° 1 foot. 2a 
Sie “ 10 in. 1 foot 6 in. 
10 “ “cc 9 “ 1 “ 3 “ 
12 “ “ g “ . 1 “ce 2 “ 
14 “ “ Tf ifs 12 “ce 
It should be observed that this table must not be taken as repre- 
senting accurately determined data at the several points on the train 
