fife Geology^ ^c. of tlit Connecticut, 



same distance. The dike along with the sandstone appears 

 to pass under a hill of greenstone. 



On the same turnpike, a few rods north-easterly of North* 

 ford meeting-house, four or five dikes occur ; but ihey are 

 so hidden by the soil as not to be particularly instructive. 

 In passing from Durham to New-Haven on the same road, the 

 first low ridge of greenstone, which we cross, exhibits some- 

 thing, which I was almost disposed to denominate a dike of 

 coarse pudding stone, of the coal formation, in greenstone. 

 Certainly, there appears a peculiar juxtaposition of the two 

 rocks; but probably they exist in beds. 



Two or three miles north of the dikes of which a profile 

 is given. Dr. Percival found several others; and perhaps 

 they are a continuation of the same. He found one also on 

 the road from Farmington to Hartford in the rocks of the coal 

 formation. 



The greenstone found in these dikes has usually the dark 

 compact aspect of basalt — resembling, however, much of 

 the greenstone found along the Connecticut. Yet it seems to 

 want the characteristics of greenstone, and specimens which I 

 collected from the most perfect dike above described, half a 

 mile east of East Rock, even approach to wacke. This rock 

 gives an argillaceous odour, is of a greenish grey color, has 

 an uneven fracture, is dull, and much softer than common 

 greenstone; so that it maybe cut with a knife: — and on com- 

 parison with a specimen of pure wacke from Calton Hill, (Ed- 

 inburgh,) which was analyzed by Dr. Webster, it does not ap- 

 pear to differ, except in its greater hardness and perhaps less 

 softness to the touch. I have little doubt that these dikes will 

 ere long be denominated basaltic dikes : but, for the reason 

 formerly alleged, I forbear to name them thus. They are 

 an interesting feature in our geology, and deserve more at- 

 tention ; and it is peculiarly fortunate that they should be 

 situated so near a geological school and the first mineral cab- 

 inet in our country. 



Juxtaposition of Secondary Greenstone and Primitive Rocks^ 



The actual contact of these has never been observed 

 along the Connecticut; and I know of bat three places 

 where there is a probability of finding the junction — viz. in 

 the northeast part of Belchertown, in East-Haven and Bran- 



