THE GRAXBY TLTFF. 



369 



(PI. XXVIII). This indicates that after the deposition of tlie major portion 

 of the cong-lomerates and the extension of the sand flats far to the east there 

 was a tilting of the beds, which gave them a slight eastward dip and deep- 

 ened the eastern channel so tliat the eastern cun-ent was sti-engthened and 

 the slate-conglomerates passed by a broad transgression west over the sands. 



ANALYSES, 



The rock of the Kibbe quany, of East Longmeadow, has been analyzed 

 by Prof. C. F. Chandler, of New York; that of the Worcester quarry and 

 of the ]\Iaynard quairy by the Worcester Polytechnic Institute. 



Analysis of the rocks of the Kibbe (/), Worce.<!ter (11), and Maynard (III) quarries. 



The amount of alumina shows that there is probably considerable 

 feldspar in the rock, and that some part of the loss is alkali. 



THE GRANBY TUFF, OR THE DIABASE-TUFF. 



This bed is the most distmct geological unit of the series. It is made 

 up of diabase ash, lapiUi, and bombs. It grows finer in any section from 

 bottom to top and from west to east. West of the Connecticut it is made 

 up of coarse material, with many masses as large as one's head. South of 

 The Notch it consists of fine lapilli, and farther east it is a consolidated ash 

 bed. It always contains some granitic material, often only muscovite scales. 

 The ti-ansition from sandstone to tuff is sudden, and the tuff rests on arkose 

 from the east end to the river, and then on fucoidal sandstone. It gi-ad- 

 uates upward imperceptibly into the fucoidal sandstone, and while the 

 main trap sheets made no impression on the sediments, the tuff furnished 

 abundance of iron and lime to all the upper beds. It is described in detail 

 in Chapter XIII, in connection with the description of the volcanic rocks. 



3ION XXIX 24 



