Crosby.] 
136 
[May 21, 
yard near the mouth of the Mystic River, in Everett, afforded 5.60 
per cent, of combined water, showing that it is nearly one-half clay 
and that the proportion of rock-flour diminishes seaward. A finely 
and evenly banded or stratified glacial clay from the vicinity of 
Concord, N. H., gave 5.80 per cent, of combined water, a sur- 
prisingly large amount considering the situation of the deposit. 
In looking about for clays that could be regarded as probably of 
non-glacial origin, attention was attracted first to the Miocene beds 
of Martha’s Vineyard. Four typical examples from Gay Head, 
collected for this special purpose, were carefully tested with the 
following results : — 
No. 1. White to gray and plastic gave 12.90 per cent, combined water. 
No. 2. Eed, variegated and plastic “ 10.40 “ “ “ “ 
No. 3. White and micaceous “ 9.85 “ “ “ “ 
No. 4. Very dark gray and carbonaceous gave 14.15 percent, combined 
water and carbon. 
No. 4 was whitened by burning of the carbonaceous matter, and 
the great loss which it suffered is certainly not all water. None of 
the samples were perceptibly reddened by ignition, showing that 
1, 3 and 4 are nearly free from iron oxide. No. 2 is, of course, 
ferruginous, but the iron is naturally peroxidized ; and since the 
red ferric hydrate would afford less water than an equivalent amount 
of pure clay, it is clear that if the iron oxide were removed from 
this sample, the proportion of combined water would be increased 
rather than diminished. A similar allowance should be made for 
the mica visibly present in No. 3. With these corrections, none of 
the samples, probably, would afford less than 11 per cent, of com- 
bined water ; showing that, but for the iron oxide, mica and carbon, 
they are very pure clays ; and in accordance with these results, 
washing affords but a very small proportion of gritty material or 
rock-flour. 
Having an opportunity to examine the Tertiary strata along the 
Potomac River, a typical example from near the base of the great 
bed of Miocene clay forming Nomini Cliffs in Westmoreland county, 
Virginia, was selected for this investigation. This clay is gray, 
and very homogeneous through a considerable thickness of the bed ; 
and it has undergone incipient lithifaction, possessing a well devel- 
oped joint-structure and not softening readily or becoming plastic 
in water. Nevertheless, it afforded 10.92 per cent, of combined 
water, thus agreeing substantially with the Gay Head clays. 
So far the indications are plain and the theory is well sustained ; 
