408 



Scientific Geology. 



concave layers of the rock (No. 1139) cleave off from the upper 

 extremity. A joint of this description will sometimes contain seve- 

 ral quarts of water ; and I have seen one of them standing by a far- 

 mer's well, which was used as a substitute for a wash-bowl ! Upon 

 the whole, I am of opinion that the form of these exfoliations de- 

 pends upon original structure, which the disintegrating agents above 

 mentioned reveal, but do not create. 



I know of no spot where so good a view of the ends of these 

 greenstone columns can be obtained, as at Titan's Pier above men- 

 tioned. They are exhibited to the best advantage on the west side of 

 the ridge, where it passes under the river : and at low water, we can 

 see the ends of the columns forming the bottom of the river, as far 

 as the eye can reach. The following sketch represents above twenty 

 of these columns, as they present themselves at low water, and close 

 to the water, at the spot just mentioned. The sides were not meas- 

 ured except by the eye, and I am confident that there is quite as 

 much, probably more regularity in the columns themselves, than in 

 the drawing. The sides, it will be seen, vary from four to six. The 

 upper ends of these columns are considerably convex : whereas only 

 one rod farther from the water, as already mentioned, they are decid- 

 edly concave. And although it is possible that in the first case the 

 form might have resulted from the action of the river, yet from all 

 that I have seen, I much doubt whether the upper or lower end is 

 uniformly convex or concave. 



Both at Deerfield and at Holyoke, one sometimes meets with co- 

 lumns that are considerably curved. In general they are not per- 

 pendicular to the horizon, but lean from 10° to 30° towards the east. 

 Hence they stand about perpendicular to the strata of sandstone be- 

 neath. 



Ends of Greenstone Columns at Titan's Pier. 



