HISTORY OF GEOLOGICAL SURVEY. 2/ 



6, chiastolite slates; 7, granite; 8, sienite ; 9, porphyritic granite; 10, quartzites; n, 

 limestones ; 12, soapstones. Little doubt remains as to the Eozoic or pre-Silurian age 

 of this entire series. 



2. Sienite of Exeter and Dover. There appear to be sienitic rocks of probable Lau- 

 rentian age, equivalent to the Ouincy sienitic group of Massachusetts, prominently 

 exposed along the Boston & Maine Railroad, between Massachusetts and Maine, 

 especially in the towns of Exeter and Dover. They form, apparently, an anticlinal 

 mass, overlaid by the Merrimack slates. 



3. Porphyritic Granite. Common granite full of large crystals of feldspar, generally 

 from one half of one to two inches long, which give a checked appearance to the ledges. 

 Some portions of it have evidently been injected ; while the arrangement of the feld- 

 spathic crystals, in parallel lines, leads to the suspicion of stratification in other cases. 

 The area is probably very irregular. 



4. Common Granite. The granite of New Hampshire seems to have originated at 

 five different periods. First are the (a) indigenous and () eruptive granites of the 

 White Mountain series ; second, the (c) indigenous granites of the Merrimack group, 

 in which none of the eruptive class have yet been seen ; third, the (d) indigenous and 

 (e) eruptive granites of the Cob's and calciferous mica schist groups. 



5. Merrimack Group. This name was informally applied by my father to the mica 

 schists, slates, and quartzites contained in the valley of the Merrimack river, in Massa- 

 chusetts. They skirt the Exeter sienites in New Hampshire, lying in troughs, on the 

 flanks of an anticlinal. They probably belong to the earliest Silurian series. 



6. Quebec Group. Lower Silurian, according to Sir William E. Logan, and largely 

 developed in northern Cob's county, the Ammonoosuc gold field, and along the Connec- 

 ticut river, chiefly in Vermont, to Bellows Falls. 



7. Cobs Group. Under this appellation, for want of a better name, are included the 

 argillaceous schists, whetstone mica schists, grits, etc., of northern Coos county, as 

 explored by Mr. Huntington, the similar and associated rocks in Barford, Hereford, 

 Auckland, etc., province of Quebec, and Essex county, Vermont, the quartzites, stau- 

 rolite rocks, micaceous schists, hornblende schists, perhaps gneiss, protogine, and other 

 rocks west of the White Mountain series and east of the Connecticut river, along the 

 whole of western New Hampshire, but excluding the calciferous mica schist (8). The 

 unity of the series, its age, thickness, and relations to the Quebec group, (8) 

 remain to be defined. It appears clearly to overlie the White Mountain series uncon- 

 formably. The calciferous mica schist and the clay slate groups seem to be limited 

 outliers. 



ACKNOWLEDGMENTS. 



The assistants of the second year were J. H. Huntington of Hanover, G. L. Vose of 

 Paris, Me., Prof. E. T. Quimby of Hanover, Prof. E. P. Barrows of Middletown, Conn., 

 T. M. Blossom of New York city, A. C. Page of Center Harbor, E. R. H. Hodgman 

 of Mason, A. A. Woolson of Lisbon, and Prof. C. A. Seely of New York. The friends 



