Trains of Boulders, in Berkshire, Mass. 318 
diminution. ‘This declension in size must be regardéd, in 
connection with theory, as a crucial. fact, wholly inexplicable 
upon the iceberg theory, which supplies no reason for such 
gradation. The masses which have travelled furthest seem.to 
be no more worn at their edges than the others, a circumstance 
in strict accordance with the theory we shall here advocate. 
The blocks have, been described as presenting no evidence 
of attrition. It Gs true, their corners and edges are not 
rounded off, nor are their surfaces smoothed and furrowed, 
like those of the tite boulders of the general drift which sup- 
ports them. Their angles are, however, perceptibly blunted 
and worn, and their surfaces all indicate a certain. amount of 
erosion. Nevertheless the boulders and pebbles of the true 
drift, below them, have a very different aspect, being entirely 
covered with the traces of a long-continued and violent 
rubbing, 
Another very curious and significant fact, already noticed 
by Dr. Reid and Dr. Hitchcock, is, that these blocks do not 
mingle with the general drift, but merely rest upon it. In a 
somewhat deep excavation on the Western Railroad, and at 
other places, the worn and furrowed fragments of the drift are 
seen to support these angular erratics, but to contain none 
below the level of the soil. The greater number of these 
angular blocks are, it is true, imbedded to a trivial depth, 
Usually an unimportant portion of their thickness. Many of 
them appear to have been suddenly split, as if by impinging 
violently upon the spots where they repose; the broken halves 
hear each other, sometimes almost in contact, sometimes 
Several feet asunder, but always with their fractured surfaces 
unworn and rough, as if the pieces came to rest very soon 
after bursting. face Se 
lt is another circumstance worthy of observation, that these 
“matics differ from the drift below them, as much in their 
mineral nature, as in their shape, size and situation. While 
Seneral drift, in any neighborhood, is composed of frag- 
Ments. torn from the outcrop of all the strata, especially the 
21 
YOL. v, 
