172 J. D. Dana—Melting of the Great Glacier. 
This unstratified drift consists of sand and gravel, with numer- 
ous scratched bowlders, without any underlying bowlder clay. 
rge bowlders are rarely met with in the stratified drift ex- 
cept near the rocky bottom on which it rests. The Triassic 
sandstone underlying the New Haven plain in some places ap- 
proaches within a few yards of the surface of the plain; and 
when so, the opening of trenches for sewers or other purposes 
brings to light a layer of gravel resting on the sandstone, which 
is full of large scratched bowlders, many over a cubic foot in 
size, and occasionally one over five hundred cubic feet. In the 
regions of unstratified drift, that is, above the level of the 
plain, bowlders are many and large, especially along the west- 
ern margin of the region; and several of trap, are between 500 
and 1000 tons in weight. 
These facts teach, as I have elsewhere remarked, that, in 
the melting of the glacier and the accompanying dropping of 
e earth and stones, the part of the material which fell over 
the dry land went down unstratified ; and that which fell into the 
waters was stratified, excepting a bottom portion made of the 
earth, gravel and great stones that were the first to drop from 
the ice. There is no evidence that the stratified drift of the 
2 
plain is newer than the main part of the unstratitied drift over 
the hills 
The stratification of the stratified drift is in almost all parts, 
except where too coarsely stony for it, of the flow-and-plunge 
style, as represented in the cuts on pages 173, 174. One of the 
arts of a layer having this structure is represented of the 
1. more oman a. Db 
the annexed cut, (fg. 1. 
BZ Zz The oblique lamination 
indicates a violent on- 
Z ward movement in the 
Sow waters; and the division 
of the layers into parts proves that there was a heavy plung- 
ing in connection with the rapid flow. A single obliquely 
laminated layer is often one to two feet in thickness, and in 
one case observed it was eight feet; and each must have been 
formed ata single onward movement of the plunging waters. 
This structure of the stratified drift hence shows that water and 
earth were let loose at the time in immense quantities; that 
there was a free flow of both which could have been well pro- 
duced through the melting and discharge of a vast glacier; and 
that, consequently there was a very rapid piling up of the 
layers of gravel and sand. ; 
Tn this oblique lamination which characterizes the deposits 
of the plain, the little laminz rise, with only an occasional ex- 
ception, to the northward ; that is, dip to the southward, and 
