THE DEERFIELD SHEET. 431 



sandstone with the vertical wall of the trap rising above. Here there 

 seems to have been no distinct basal bed, bnt the whole mass was cooled 

 nearly to the crystallizing point when the sand rose np into it at almost 

 equal intervals, and the streams of the sand and glass breccia formed by 

 the water rise in great streaks or "schlieren," anastomose, and pass with 

 fluidal stracture ai'omid the great rounded blocks of the nornial trap, which 

 make somewhat more than half the wall. 



At the quarry is a more distinct basal lied of trap 7 oi- 8 feet thick, 

 more or less shattered and displaced, and the sand can be seen continuous 

 with the underlying sandstones rising in rifts in this basal bed and frotliing 

 out into a scoriaceous sandstone, where it meets and blends with the breccia 

 above. This breccia is 60 feet thick — a greenish mass of shattei'ed glass and 

 trap, full of filaments of red sand shining with hematite scales. 



The rounded, bomblike masses of the compact and crystalline trap 

 which are contained in this breccia grade superficially thi'ough hyalopilitic 

 trap into the gi*een glass, and while compact at center are toward the sur- 

 face full of radiating steam pores. They seem to have been often carried 

 aloft by the explosions into the still liquid glass, partially melted, and made 

 superficially plastic by reheating, so that the steam has been able to struggle 

 to the surface from the outer portion. Where they are large and angular 

 they have been earned but a little way from the base where thev were 

 formed; where they are small and spherical they are far-carried and nmch 

 resorbed in the glass mass. 



Among these blocks are many long sheets and rounded masses con- 

 nected by narrow necks, which could not have been blown into the air and 

 have fallen as common bombs. (See PI. VIII «, p. 4:2G.) 



A little way north of the quan-y one can climl) up tlie whole face of 

 the trap by a steep path, and GO feet from the base can study the top of 

 the breccia. Here are unusually large masses of sand frothed up into an 

 amygdaloidal sandstone and filled with water-deposited silicates like the 

 Cheapside rock (see PI. VIII c, fig. 3), and above this the trap is normal and 

 crystalline and full of steam holes for a few feet, and then grades into the 

 common compact columnar trap of the upper part of the sheet.^ 



' Inreportiugmy brief account of this case, Professor Dana has destroyed the meaning of the whole 

 by an error. He says that the trap sheet rests ou coarse sandstone-breccia 12 to 16 feet thick, instead 

 of coarse trap-breccia. (Manual of Geology, 1895, footnote on p. 805.) 



