B. K. Emerson — Cylinders of Scoriaceous Diabase. 321 



Art. XXI. — Description of Large Cylinders of Scoria- 

 ceous Diabase in the Normal Holyoke Diabase y by B. K. 

 Emerson. 



There has been in the Amherst College Museum for many 

 years a great block of diabase labelled " Tuff with tree trunks, 

 from Amherst." It is described by Prof. C. H. Hitchcock in 

 " Guide to Amherst College Collections 1862.'" 



It is a great bowlder and came doubtless from the trap sheet 

 in Deerfield Mountain several miles north of Amherst. It is 

 2 ft. by 1 ft. by 9 inches, and has been much broken in devel- 

 oping the tubes. A smaller piece, apparently broken from the 

 main mass, is 22 inches by 6 inches by 9 inches. The rock 

 must have been called tuff without careful inspection ; because 

 the tubes simulate small straight tree trunks so perfectly, the 

 inference was made that the enclosing rock must be tufaceous. 

 A thin section showed it to be the normal diabase of the Deer- 

 field bed, and a section of the tubes showed a greatly decom- 

 posed diabase with a fibrous monoclinic zeolite, apparently 

 scolecite, filling the cavities. 



There are two of these cylinders on one side of the big block 

 and one on the other; and one on the smaller block (see fig. 1). 

 They are straight and closely parallel with each other, and 

 taper exactly like a tree trunk. One nearly circular cylinder 

 is 2 1/8 inches at one end and 1 1/2 inches at the other. 

 Others are slightly flattened, fluted or in places triangular with 

 rounded sides. One is 3 inches by 1 1/2 at one end and 2 

 inches by 1 1/2 at the other. The longest tube is 22 inches in 

 length and broken off at both ends. They are scoriaceous the 

 whole length but mostly so on the outside. The cavities are 

 small, averaging about 3/16 of an inch. 



Recently a smaller piece three inches long was found as a 

 bowlder about a mile southeast of the Mount Holyoke House, 

 where it could easily have been brought from the Deerfield 

 sheet. It is 3 inches long, 1 1/2 by 3/4 at one end and 1/2 

 inch in diameter at the other, and with coarser and thicker 

 steam holes. The containing rock is a quite coarse diabase, 

 with many porphyritic feldspar crystals, much like the coarser 

 portion of the Deerfield sheet. 



The Deerfield sheet is composite, at least two bands of scori- 

 aceous rock occurring in the central portion of the mass. The 

 enclosing rock in the two blocks is a diopside diabase of the 

 same type as the rock at the upper surface of the sheet at the 

 Lookout above the city quarry in Greenfield, where the large 

 quantities of the subjacent wet sand were carried explosively 

 up into the central portion of the sheet from below.* 

 *Bull. Geol. Soc. Amer., vol. viii, p. 59, 1897. 



