THE DEERFIELD SHEET. 439 



The sudden introduction of so large a volume of water has caused the 

 mass to cool as a spherulitic glass with a minute crackling, which gives it 

 a pitchy luster and a large content of water (4.72 per cent), thus forming a 

 basic pitchstone, which does not seem to have been described before. 



As a further direct influence of the water on the lava, many abnormal 

 forms of trap were made locally. The liquid mi;d rose in the liquid lava 

 with many explosions, shattering the abnormal mixtm-es already solidified, 

 and blending them in still more complex nuxtures while the newly solidified 

 glass was still slightly plastic. 



The whole is cemented by the renmaut of the glass, or an aqueo-igneous 

 stage follows the igneo-aqueous, and a more distinctly hot-water product, 

 consisting of albite, diopside, hematite, calcite, and aegerine-augite, forms 

 the cement. This glass-breccia is proved to be an integral portion of the 

 trap sheet by the fact that there is a heavy basal bed of crystalline trap 

 resting upon the sandstone, and the breccia gi-ades downward into this 

 bed, as it does also upward into the overlying crystalline trap which forms 

 the major portion of the overflow. Sometimes this basal bed is sliattered 

 and its parts are carried up into the glass and rounded and filled with 

 superficial steam holes by remelting. 



CONTACT OF THE SANDSTONE UPON THE DIABASE. 



On either side of the mouth of Fall River, and for a mile south, con- 

 tinuous outcrop of the upper contact is visible at low water. The rather soft, 

 deep-red, shaly sandstone is wholl}' unaltered and never included in the trap, 

 while it folds around all small protuberances of what was, doubtless, the old 

 ropy surface of a lava flow, its laminae thickening in the bottom of the pro- 

 tuberances till they have evened up the surface of the ropy lava, and at 

 times fragments of the traps are wholly included in the sand. The sand 

 even fills the opened steam holes. Just north of the point where the wood 

 road goes east from the Sunderland Hotel there is another fine contact of 

 the sandstone on the trap, near its south end. 



FALL RIVER FAULT. 



On following down the trap from its north end to the Connecticut, 

 one finds that it halts abruptly at the water's edge east of the mouth of 

 Fall River and faces an island of sandstone which lies just in its line of 

 stiike; but on following the bed up from the south, one discovers that it 



