NEW HAMPSIIIRE. 



393 



Waabiiigton Eiver, .... there is a limited synclinal of osaipytc rcating upon 

 the upturned edges of the andalusite gneiss." (Proc. Bost. Soc. Nat. Hist., 

 1873, XV. pp. 304-310.) 



In the second volume of the New Hampshire Geology, Prof. Hitchcock 

 writes as follows : — 



" Another important doctrine relates to the identification of formations in 



our field of labor by means of mineral characters The style of sinular- 



ity made use of for identification is better shown in the porphyritic gneisses. 

 There are over thii'ty areas of porphyritic gneiss, in which the feldspar crystals 

 are very conspicuous for their size, the rock being the Augen gneiss of Europe I 

 assume that all the areas of this rock are identical in age, and, in speculatnig 

 upon the relative positions of the intervening groups, rely upon the correctness 



of this starting point The fact of minor differences would seemtocon- 



firm our assumption of their identity in age, just as the paleontologist finds, 

 from the presence of the same fossils, proof of contemporaneity in rocks with 

 dissimilar mineral character. From these facts [the supposed relations of the 

 rocks] it is inferred that the porphyritic gneiss is older than either the Lake or 



the Montalban gneisses, the last being the newest It may as well be 



said now as at any time, that nothing older than the porphyritic gneiss has 

 yet been discovered. This formation constituted the first drv land in the 

 state." {I. c, pp. 659, 660, 663, 664.) 



The equivalency of the New Hampshire formations with others Is in 

 part stated as follows : 



" The first two of our groups may be referred to the oldest of these, the Lan- 

 rentian, without great hesitation A porphyritic or augen gneiss is emi- 

 nently characteristic of the fundamental rocks in every part of the world, and 

 hence ours may readily be called Laurentian. ..... Those who are familiar 



with the crystallines, as Prof. Dana and Ur. Sterry Hunt, after examining some 

 parts of the Bethlehem group in New Hampshire, say that there is a close 



resemblance between them and the Laurentian I have grouped these 



rocks, the porphyritic and Bethlehem gneiss, as Laurentian. 



" The next division, the Lake gneiss, cannot be so readily assigned. Its 

 affinities are strongly with the Laurentian, but it is not pyroxenic nor porphy- 

 ritic, nor does it abound in any triclinic feldspar In Massachusetts this 



group carries the Eozoon^ but that fossil is not confined to the Laurentian. 

 . . . . The Montalban series are certainly not characteristic of the Laurentian. 

 , . . . Dr. Hunt ia satisfied that they overlie the Huronian or greenstones. 

 Our own observations lead to the view that the typical Montalban rocks un- 

 derlie the same, as recently stated, though the precise relationship is not beyond 

 controversy." (I. c, pp. 668, 669.) 



The other formations are in like theoretical manner referred to their 



r 



r 



supposed places, with the exception of the Helderberg series. 



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ft. 



