MUSEUM OF COMPARATIVE ZOOLOGY. 131 
sheets ; but, on the other hand, the sandstone might also, until its con- 
tinuity in bands across the quarry was noticed, be regarded as fragments 
of sandstone picked up and included in the trap at the time of its erup- 
tion: not that such inclusions would necessarily indicate intrusion, for 
extrusive sheets are well known to contain fragments oft he adjacent 
country rock. 
The general attitude of the several bands of breccia negatives the 
second interpretation. The bands all maintain a straight course 
through the quarry; a single band may cut the lower, as well as the 
upper sheet ; the bands stand at right angles to the general extension 
of the sheets ; they are parallel to one another and to the course of the 
large faults by which the region is broken. The dividing surface be- 
tween the lower and upper sheet in the southern end of the quarry is 
seen to be dislocated by one of the bands, with small heave on the east, 
this being the relative displacement of the large faults in the region. 
Neglecting this sufficient series of indications of their origin, we ex- 
amine their structure more closely, and discover that they are fre- 
quently slickensided, and that the trap fragments that they contain are 
sometimes broken since taking their places in the bands. Moreover, 
these trap fragments are themselves included in the sandstone matrix 
of the bands ; the fragments are angular, and show no variation of tex- 
ture from centre to surface; the sandy matrix contains small broken 
grains of sandstone, as well as of sand. Again, if the sandstone which 
accompanies the trap fragments had been picked up and included in the 
main mass of trap at the time of eruption, it should present evidence of 
the action of heat, as in induration, or more likely in some alteration, 
for the relatively small areas of sandstone in so large a mass of trap 
must have long been subjected to intense heat. With this idea in 
mind, a comparison was made of sandstone from the breccia bands with 
a block of sandstone in a large dike a little north of Mount Carmel 
station, New Haven and Northampton Railroad, locality 27, to which 
Professor Dana had called our attention. The blocks of sandstone in 
this dike are five or six feet long and two or more wide. When struck 
with a hammer they give a ringing sound, characteristic of induration. 
Sections of the sandstone show it to be principally composed of quartz 
grains mixed with fragments of feldspar, and closely cemented by a 
clayey material. While it exhibits no significant alteration in composi- 
tion from ordinary sandstone, it cannot be doubted that its exceptional 
density was the result of the dehydrating action of heat from the molten 
dike on the kaolinite that formed the clayey cement. The contact of 
