1879.] 317 {Wadsworth 
broken before the matrix can be removed. The pebbles of course 
break with a conchoidal fracture, and must have done so under the 
pressure of the glacier. This fracture will account for the peculiar 
form of the upper surface of many of these pebbles. I believe that 
glaciation and the action of water and sand since, have caused the 
markings that Mr. Crosby claims to have been formed by the pres- 
sure of one pebble into another when plastic, and by the slipping of 
one over the other. 
As far as I have been able to ascertain by examining the locality 
carefully several times, it is true that while these forms can be seen 
by the thousands on the glaciated surface, not one can be found in 
the interior of the conglomerate nor where the surface was removed 
some years ago by quarrying. While Mr: Crosby contends that very 
many of the forms were made by the sliding of one pebble over 
another, I can hardly imagine that so much sliding could have taken 
place at the present surface and no where else in the conglomerate. 
While the bedding is uniform and inclined to the surface, the flattened 
planes of the pebbles are generally parallel to this surface throughout 
its contours, and the rounded edges conform in like manner to it, 
never extending below the matrix. These forms are found on soli- 
tary pebbles, in the coarse sandstone at this locality, on the glaciated 
surface where we have not the slightest reason to suppose any pebbles 
have existed to indent them. The flattening (so called) has taken 
place on the upper surface while the lower side of the pebble retains 
its normal form. Many of these pebbles are fissured and the fissures 
filled with crystalized quartz. This fissuring it is claimed took place 
at the time of the flattening and indentation of the pebbles, but I find 
that the supposed indentation has gone into the fissures, removed the 
quartz and polished their walls at the upper part. Some of the 
polished forms that are exhibited to-night are in such angular and 
irregular shapes that it seems impossible that they could have been 
made by the pressure of one pebble into another. As these pebbles 
are composed of little sand grains they are conglomerates on a small 
scale, and doubtless have been compressed as any fragmental rock is 
liable to be. The indentations supposed by me to have been pro- 
duced by pressure at this locality are little rounded depressions 
entirely unlike the forms shown here. Ifthe pebble had been plastic 
and squeezed, as it is claimed, the grains of sand, being thus plastic, 
would have been flattened and drawn out. Signs of the pressure 
