52 Geology, ^c. of the Connecticut, 



form are often a foot or more in length, and arranged par- 

 allel to one another; the rock appearing as if bored through 

 repeatedly by an augur. The imbedded minerals are cal- 

 careous spar, analcime, chlorite, quartz, chalcedony, chaba- 

 sie, zeolite, and Professor Silliman has recently discovered 

 gypsum* in a specimen sent him from Dr. Cooley ; a new 

 fact we believe in Geology, and one which renders it not 

 improbable that this valuable mineral may be found in abun- 

 dance along the Connecticut. 



This amygdaloidal greenstone is probably most abundant 

 at the lower part of the greenstone ridges ; while the upper 

 part is solid and usually columnar. Frequently, however, 

 the columns are amygdaloidal to their top, and sometimes, 

 as in Deerfield, in passing in the direction of the ridge, you 

 will find alternate successions of amygdaloidal and solid 

 greenstone columns. On breaking into the interior of the 

 former, we often find them a rich reservoir of rare miner- 

 als. The cavities are usually small; but sometimes sever- 

 al inches in diameter, occupied by quartz and amethystine 

 geodes, or chalcedony, or agates, or a peculiar pseudo- 

 morphorus quartz to be described when we come to treat 

 of particular minerals. The largest and best agates occur 

 usually among the greenstone that is not much amygdaloid- 

 al, sometimes occupying a cavity, part of which is in one 

 column and part in another. They are very frequent, and 

 some of those recently discovered by Dr. D. Cooley, in 

 Deerfield, are probably the finest yet found in this country. 

 A particular account of them will be given in the proper 

 place. Prehnite sometimes forms a thin incrustration on 

 the columns that are not amygdaloidal; and between the 

 joints of those that are so, is sometimes interposed a thin 

 coatingof various minerals, among which epidote frequently 

 predominates. 



Some of the amygdaloid is very vescicular, bearing some 

 resemblance to the slag of an iron furnace or lava. The 

 cavities, in certain rare varieties, are various in form ; and 

 the base is whitish brown, reddish, and even brick red ; 

 containing, in the cavities, much prehnite, and this mineral, 

 together with calcareous spar, seems, in some instances, to 

 be mixed with the greenstone to form the base. An en- 

 thusiastic Huttonian would doubtless be gratified to find 



*This gypsum was perfectly fresh — crystalized — white, and retaining^ its 

 water of crystalization. — Editor. 



