440 



Scientific Geology. 



of Mount Holyoke, and in the pastures by the road side, he will see 

 hummocks of amygdaloid so much resembling lava, as to remind 

 him of the Phlegrean Fields. And a similar appearance is not un- 

 common in other spots on the east and southeast sides of Holyoke 

 and Tom. 



Some writers regard the minerals peculiar to our greenstone, such 

 as chalcedony, the zeolites, prehnite, augite, &c. as evidence of its ig- 

 neous origin. But if, as is probable, most of these were infiltrated 

 from solution in water, this proof is not of much weight, especially 

 since they have been found of late in several of the stratified rocks, 

 such as mica slate, gneiss, &c. though I am not aware that they have 

 ever been discovered in rocks of exclusively aqueous origin. 



2. The columnar structure of greenstone. The same columnar 

 form is assumed by lavas when they are slowly cooled ; but in no 

 case by rocks of known aqueous origin. How unphilosophical then, 

 to refer this structure to aqueous agency ! 



3. The irregular mariner in vihich greenstone is intruded among 

 stratified rocks. Water and fire are the only two great agents in na- 

 ture, as I suppose will by all be admitted, sufficiently energetic to have 

 produced mountain masses of rock ; so that we must take our choice 

 between them, unless we can show that both of them were concerned 

 in the work. Now I cannot conceive it possible how any logical 

 mind, that has observed trap rocks in situ, or will attentively consider 

 the manner in which I have shown our greenstone to be intruded in 

 the form of veins and irregular masses among the stratified rocks, 

 can conceive how they could have been deposited in these modes from 

 water. But they are exactly the shapes which melted matter, forced 

 from beneath, through and among consolidated strata, would have as- 

 sumed. What but a wedded attachment to hypothesis, then, can pre- 

 vent us from admitting their igneous origin ? 



4. The Mechanical effects of Greenstone upon the Stratified Rocks. 

 I refer here to the evidence that our greenstone has elevated, broken, 

 and dislocated the strata in some instances through which it has been 

 protruded. The section at Turner's Falls, exhibits a good example of 

 these effects, as well as similar effects of the primary rocks, which 

 will be noticed farther on. Nearest the greenstone on the upper side, 

 we find the dip to be greatest, gradually diminishing as we recede 

 from the ridge. That this increase of dip resulted from the protru- 

 sion of the greenstone, is evident, it seems to me, from the fact that 

 beneath that rock the dip is less, corresponding to that of the forma- 



