438 GEOLOGY OF OLD HAMPSHIRE COUNTY, MASS. 



been carried into the mass with the mud, that there is ahnost no trace of 

 amygdahiidal deveh)})ment. Onh' one fragment of a trap inclosed with 

 others in a bi-eccia contained small steam holes. 



The collapsed cavities with wrinkled interiors and the absence of the 

 common steam holes are explained by the absorption of the water by the 

 magma, and this absorption explains the unusually large development of 

 basic glass in c<innection with this exceptional occurrence. Above the 

 compact and columnar trap which rests on this hydrated glass is the usual 

 coarsely amygdaloidal surface layer of the trap, whose moisture seems to 

 have no connectio'n with this development at the base of the bed. It was, 

 however, in this surface amj^gdaloid in the Deerfeld bed that I found 

 perfect secondary albite crystals resting on diabantite in the amygdules. 



The great abundance of calcite and its intimate admixture with the 

 other constituents are remarkable. I have elsewhere given reasons for 

 thinking it in great part formed during the consolidation and cooling 

 of the glass It is consonant with this that the feldspars formed dm-ing 

 this cooling, esiteciall}- those in the spherulites, are quite acid, while Hawes 

 found xerj basic feldspars an abundant constituent of normal trap. 



When these secondary feldspars are boiled with strong hydrochloric 

 acid and treated with fuchsin there is no trace of decomposition, and the 

 optical characters indicate a very acid feldspar. The CO* brought into the 

 mass by the waters from the coal-bearing sandstones below may have taken 

 possession of a large portion of the Ca, leaving the Na to go into the newly 

 made feldspar. 



The similarity of this aqueous feldspar to that in a metamorphic schist 

 is remarkable, and it is interesting to find diopside and a?gerine-augite and 

 hematite formed with it, thus making a very peculiar crystalline schist in 

 a very peculiar position. 



It is again remarkable that diabantite and its seipentinous decomposition 

 pi'oduct are rare in these glasses and the associated traps. This militates 

 against the idea that the penetration of the ground waters into the liquid 

 tra]) is the cause of its chloritization. 



The lava bed flowed over the muddy bottom quite rapidly, and the 

 heated mud and water have frothed up into the still liquid mass, causing an 

 intimate blending of sand and lava for a thickness above the base of the bed 

 of from 30 to 75 feet and for a distance, i)arallel to the advancing front of 

 the sheet, of several miles. 



