HISTORY OF GEOLOGICAL SURVEY. 4g 



crinoidal stems. Mr. Billings reports that the brachiopod is allied to the 

 Pentamenis Knightii of the Lower Helderberg ; and that the gasteropod 

 is also like one in the same formation. The crinoidal fragments place 

 this deposit in correlation with the noted bed at Bernardston, Mass., first 

 described by my father in 1833. Geologists had supposed the latter bed 

 to be of Devonian age, because the large crinoids seemed like those from 

 the Corniferous beds in New York ; but our discoveries serve to modify 

 this conclusion. Considerable attention was devoted to the Helderberg 

 deposits by us in 1873, and we have been enabled to derive most impor- 

 tant generalizations respecting the structure of the state, second in 

 importance only (though most would value them more highly) to the 

 results of the White Mountain exploration. A lengthy sketch of the 

 New Hampshire Helderberg rocks has been published in the American 

 youmal of Science for April, 1874. Our next volume will treat the sub- 

 ject with all the detail required. 



QUARTZITES IN THE GnEISS. 



Hon. S. N. Bell, of Manchester, pointed out to me, before commenc- 

 ing the New Hampshire survey, the occurrence of interesting bands of 

 quartzite in the southern part of the state. As soon as occasion offered, 

 an examination of them was commenced. Mr. Bell often accompanied us 

 on our expeditions, and for his own pleasure traced out thirty or forty 

 miles of their extent. In 1 871, in company with Mr. L. Holbrook, the 

 limits of these bands were studied in Hillsborough, Merrimack, and 

 Strafford counties. The results of our examination indicated that these 

 two bands of quartzite traverse a tract of country, often in a serpentine 

 course parallel to each other, eight or ten miles apart, from Temple to the 

 north part of Strafford on one line, and from New Ipswich to the south 

 part of Strafford on the other. Beyond this point the formations seem 

 to be covered by the andalusite schists. 



After passing a wide band of gneiss to the west of the Temple-Straf- 

 ford range, we came to a belt of porphyritic gneiss, which seems to be 

 the oldest formation in the state. In accordance with this view of the 

 relative ages of the formations, we find similar rocks west from this cen- 

 tral porphyritic gneiss. The studies commenced by G. A. Wheelock, of 

 Keene, have brought to light two beds of the same quartzites in Keene 

 VOL. I. 7 



