HISTORY OF GEOLOGICAL SURVEY. I/ 



structure of all New England. A portion of the map was enlarged, and 

 hung upon the wall of a room at the state house, near a case of speci- 

 mens, where those who were interested in the subject could judge of 

 the correctness of the conclusions. 



The description states that "there are two general divisions upon the 

 map : first, the granitic and gneissic rocks, which appear to be older, and 

 consequently to underlie the formations of the second or Quebec group? 

 Explanation is then made of the term "Quebec group," and its use in the 

 sense in which it was proposed by Sir W. E. Logan stated to be "provi- 

 sional, and liable to amendment after further explorations shall have made 

 our knowledge more definite." 



The historical importance of the description of the map leads me to 

 quote it : 



A mere glance at the map and accompanying section suggests two conclusions : 

 First, there is an unusual expansion of the area occupied by the gold rocks north of 

 Haverliill, which contracts to some extent in the latitude of Littleton. The narrowest 

 part of the group can be seen by referring to the Vermont Geological Map, and notic- 

 ing the contracted band, not three miles wide, along Connecticut river. It is not over 

 four miles wide in any part of its course between Lebanon and Woodville. 



Second, the rocks assume the form of a basin or synclinal axis.* To confirm this 

 view, appeal is made to the general arrangement of the several groups. In the centre 

 is the auriferous conglomerate, with some of the upper schists. These are inclosed by 

 a line of dolomite, not represented upon the map ; this by clay slate ; the slate by the 

 lower green schists which occupy the outer edge of the basin, and adjoin the gneissic 

 rocks of the White Mountains upon the east, and the calciferous mica schist or supposed 

 upper Silurian strata on the west in Vermont. Hence the strata in the centre of the 

 field, the conglomerate, slates, and upper schists lie at the summit of the series, and 

 were the latest formed. A few words about each sub-division. 



1 . Gneissic and Granitic. These rocks consist of gneiss passing into mica schist 

 and granite. They continue easterly from the gold-field past the White Mountains into 

 Maine. By way of geographical convenience, they may be called the White Mountain 

 series. The line of union is irregular, and the bordering rock is not uniform. In Lit- 

 tleton it is generally granitic ; in Lisbon, gneissic ; more quartzose in Haverliill. A 

 bed of limestone skirts the border in Lisbon, and its place seems to be taken by soap- 

 stone in North Haverhill. 



2. Staurolite Rock. Adjoining the gneiss, and apparently resting upon it, is a slate 

 or schist (according to locality) filled with crystals of the mineral staurolite, called 



* Shown also farther north. Geology of Vermont, p. 521. 

 VOL. I. 3 



