482 ON THE PHYSICAL STRUCTURE 



The next notice in the order of time of this structure is, that 

 given by Prof. Hitahcock in his Elementary Geology, published 

 in August, 1840. In this work. Prof. H. refers to our published 

 observations respecting the extensive inversion of the strata in 

 Pennsylvania and Virginia, and proposes to explain the prevail- 

 ing southeasterly dip in western Massachusetts, and the Hudson 

 river district, by the hypothesis of a simple but vast inversion of 

 all the rocks extending entirely across the region in question. 

 This explanation, accompanied by a short section through the 

 Hoosic and Taconic mountains, is given as an instance of I'wyer- 

 sion, and not of the folding' of strata, the latter subject being 

 discussed separately on another page. 



At a meeting of the American Philosophical Society, on the 

 first of January, 1841, one of us communicated the results of some 

 observations upon the geological structm'e of Berkshire, Mass., 

 and the neighboring parts of New York, which we had made 

 during the month of August previous, and gave an outline orally 

 of our theory, explanatory of the phenomena. After adverting to 

 the statements of previous writers, that all the strata between the 

 Hoosic mountain and the Hudson river, lie in an inverted order, 

 drawings were exhibited, proving the existence of numerous 

 closely-folded anticlinal and synclinal axes ; and the inference 

 was di-awn, that the inverted dip of the rocks is the result of a 

 folding of the beds at short intervals, and not of one general turn- 

 ing over of the whole series, as suggested by Prof. Hitchcock. 

 Subterranean igneous action was referred to as having caused 

 this compression and folding of the rocks, and its energy was 

 shown to have been greatest along the Berkshire valley, and the 

 ridges lying to the east. To the same agency was attributed the 

 crystalline condition of the Berkshire marble, and of the associa- 

 ted schists and semi-vitrified quartz rock, the first being regarded 

 as merely the blue limestone of the Hudson valley, extensively 

 altered, and the last a highly altered form of the white sandstone 

 at the base of the Appalachian formations.* 



In the following April, Prof. Hitchcock, in his very able address 



* See Proceeding's of American Philosophical Society for January, 1841. 



