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 tiie 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 



