148 B. K. Emerson — Proofs that the Holyoke, etc. 



out of the depressions and slowly obliterate them, and all with- 

 out marked induration. The trap immediately beneath is the 

 finest amygdaloid. This is a portion of the posterior sheet. 



5. The Holyoke sheet is covered by arkose and this by a 

 thick bed of trap tuff and agglomerate whose outcrop stretches 

 parallel to, and a mile south of, the main Holyoke sheet from 

 its east end to Holyoke town, about eighteen miles. 



I have cut many thin sections from all parts of this bed, and 

 the diabase of which it is composed is not in any way to be 

 distinguished from that of the main trap sheets here discussed. 

 This makes certain the eruption of a great amount of trap 

 during the deposition of the sandstones, and accords with the 

 supposition that the closely associated Holyoke sheet was also 

 contemporaneous with the sandstones. Fig. 2 gives a sketch 



of the east end of the Holyoke range and shows that the trap 

 sheet and the tufa bed have been faulted together and that the 

 main trap sheet must have found its present place in the sand- 

 stones below the tufa before the epoch of disturbance which 

 caused this faulting, while the latter cores show generally a 

 distinct connection with these faults. 



Except the Holyoke and Deerfield beds, and the "posterior" 

 trap sheet running across Holyoke town and Agawam, all the 

 trap given on the small map recently published by me* is 

 intrusive but is in small amount, and is in every way contrasted 

 with the large beds discussed above. The intrusive trap sends 

 out dikes in the sandstone in all ways. The smallest cores or 

 dikes do much more baking than the thick beds because they 

 have passed as hot lava through the sandstone while the beds 

 have run as scoria-encased flows on the sands. 



* Bulletin of tlie Geological Society of America, vol. ii, pp. 451-456, pi. 17. 



