252 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
somewhat prominent lamination shown by the sandstone in places, 
and the well-developed cleavage in the more shaly portions, both 
tended undoubtedly to furnish an unusually large number of 
boulders. The abrupt ending of the red series on the east made it 
possible to lay down with considerable exactness the eastern bound¬ 
ary of the train, but the extent of the series unfortunately prevented 
the making of similar observations on the western border. 
o 
Boundary of Train. 
When the work of determining the boundary of the red Carbonif¬ 
erous boulder train was first undertaken, it was believed that a 
careful examination of the stone-walls for red boulders would give 
results sufficiently accurate for all practical purposes. A boundary 
based on such data was, in fact, worked out and is indicated by 
the dotted line on the map. It was found, however, on examina¬ 
tion of exposures of till, that red pebbles, and even boulders, were 
to be found in places at a distance of a mile or more outside the 
boundary thus determined, and it became necessary, therefore, to 
redetermine the boundary, basing it upon a careful study of the 
till wherever exposed. This boundary (represented by the full line 
on the map) starts at the same point as the other, and for a mile 
and a half, or as far as North St., is coincident with it. From 
this point on, however, the easting of the latter is greater, increas¬ 
ing rapidly to about 55°, and passing just north of the railroad 
junction at Mayflower Park. Beyond the railroad the bearing of 
the boundary continues to change rapidly, increasing from S 55° E 
at the railroad to S 65° E just north of Cranberry Pond, and to 
nearly S 80° E at the South Weymouth station, beyond which it 
was not studied. A straight line drawn from the easternmost source 
of the red boulders to the South Weymouth station would bear 
approximately S 60° E and would, at its middle portion, lie about 
three quarters of a mile north of the boundary as determined by 
observation. 
It will be noticed from a comparison of the two boundaries on 
the map that the difference between them increases rapidly as the 
distance from the source of supply of boulders becomes greater. 
This is evidently due to the rapid decrease both in the number and 
size of the boulders which renders them less likely to be represented 
in walls. 
