Geology, ^c. of the Connecticut: 61 



er a sandstone of the coal formation, this greenstone must 

 be regarded as a bed between them.* 



14. Coal Formation. 



Variety of Psammite. Brongniart. 



Grey Wacke Slate, Eaton. 



Colored brown by Umber. 



It has long been known to mineralogists that coal was 

 found along the Connecticut ; and I denominate the rocks 

 containing it the coal formation, simply because its beds 

 occur in them, and in no other rock; the old red sandstone 

 containing none at all, but lying below it. The coal forma- 

 tion embraces numerous varieties and sub-varieties of rocks, 

 most of which alternate with one another and the principal 

 of which are the following. I. Greenstone. This strictly 

 belongs to this class because it alternates with the other va- 

 rieties and in Berlin contains coal. But there were suffi- 

 cient reasons for giving it a separate color and description, 

 which it is unnecessary here to mention. 2. Trap, Tuff, 

 {Trap Breccia, Cleaveland.) This occurs on the east side of 

 Mount Tom on the west bank of Connecticut river, and ap- 

 pears to lie between other rocks of the coal formation and 

 the greenstone, and perhaps alternates with the greenstone ; 

 though I cannot say much as to its geological relations, as I 

 have but recently discovered the rock and have had little op- 

 portunity to examine it. It consists of rounded or angular 

 fragments of greenstone, quartz and sandstone, united by 

 a reddish brown abundant cement of comminuted and de- 

 composed sandstone, greenstone or wacke. Scales of mica 

 appear scattered in the rock which seem to have belonged to 

 the sandstone. It exhales an argillaceous odour, is difficult to 

 break, and is about of the hardness of old red sandstone. The 

 imbedded masses of greenstone are larger than the quartz 

 or sandstone. I noticed some, six, eight, and even twelve inch- 

 es across. Perhaps this rock is not the real trap tuff of Eu- 

 rope. If not, it certainly deserves the name of greenstone 

 conglomerate: although many of the imbedded masses and 



* Some other corrections needed to be made in the essay accompanying 

 that profile and map. But as I intend to comprehend all that is important 

 in that paper in this Sketch, a particular specification of corrections seems 

 Hnnecessary. 



