Niles.] 2 [January 3, 
upon the surfazes. The position of these crystals bore no relations 
to the size, form or character of the pebbles, but was always directly 
related to the position of the pebbles in the rock. An imaginary line 
passing from one centre of crystalization directly to the other, while 
the pebble was in position in the rock, would represent correctly the 
direction of the dip of the stratum. Among the hundreds of speci- 
mens examined, this relation between the position of the crystals upon 
the pebbles and the inclination of the strata, was found to be invaria- 
ble. He believed that this indicated the cause of the metamorphism, 
and that the physical force which elevated the strata was likewise 
concerned in determining this constant position of the crystals. It 
was clearly evident that some of the pebbles had been subjected to a 
pressure, as they were often curved, broken and elongated, as Hitch- 
cock and others had observed at other localities. Moreover, the whole 
rock was somewhat metamorphosed. It seemed to him in this in- 
stance, at least, pressure must have been the chief cause of the first 
crystalline metamorphism of the pebbles, as it was also the cause of 
the well known metamorphism of form. But he was not prepared to 
explain the chemical change which had taken place. He had ob- 
served that there were often cavities between these pebbles and the 
surrounding rock, at just these two points where crystallization 
appeared, and vet the crystals had so firmly united them with the 
matrix as to often make it difficult to separate them, though at other 
points upon: the surface the separation was comparatively easy. 
He exhibited some pebbles which had been broken, the parts 
slichtly displaced and then united by crystalization. He hoped 
some of the members present might explain why the usual chemical 
changes had been apparently limited to these two centres of crystal-- 
lization. 
Prof. Shaler said he had observed a similar feature in the 
rocks in Switzerland, and had found there cases of the pene- 
tration of softer rocks by those of harder substance. He 
thought that the elongation of some pebbles might be due to 
lateral pressure; this would tend to produce cavities at the 
extremities of the longer axes of the pebble. He had had 
opportunities of studying this subject in the Newport con- 
glomerate in the neighborhood of Black Point. 
