148 STRATIGRAPMICAL GEOLOGY. 



are also a few remarks about the eruptive rocks of Jackson and vicinity 

 upon a previous page. 



Rocks .South of the Saco River. 



liY J. H. HUNTINGTON. 



Feldspar-porphyry and breccia. If a person Vvcre to study the rocks 

 of the mountain region of New Hampshire only along the travelled 

 roads, he would not only get an imperfect, but also a very erroneous 

 idea in regard to the geology of this section of the state; and there is 

 no one point where a person would seem to have better data from which 

 to draw conclusions than from the examination of the rocks along the 

 Saco in Bartlett, and Swift river in Albany. At a point on the Saco we 

 have a granite composed largely of feldspar; and at a place on Swift 

 river, directly opposite, we find the same kind of rock, — so it would seem 

 reasonable to conclude that this is the rock between these two points; 

 but a person who came to such a conclusion would be very much mis- 

 taken. Finding the granite in Bartlett, opposite the mouth of Stony 

 brook, we follow up that stream. Three fourths of a mile from the road, 

 the first outcrop of rock we find is a feldspar-porj^hyry, which is com- 

 posed in part at least of a triclinic feldspar. This extends probably a 

 mile; and the jointed structure of the rock gives to it the appearance of 

 stratification. This rock is followed by a breccia and porphyry; in the 

 latter frequently there are small crystals of a flesh-colored feldspar. The 

 feldspar crystals continue to become more abundant, until the rock is 

 hardly distinguishable from a reddish gneiss, yet a careful examination 

 shows that mica is wanting. Near the height of land the rock changes, 

 and is composed apparently of a compact feldspar, with a little quartz. 

 Descending from the height of land towards Swift river, joerhaps a fourth 

 of a mile from the summit, and on the main branch of Little Deer brook, 

 the rock is a distinct breccia, which is of a dark color, having a feld- 

 spathic paste, and pebbles of labradorite, porphyrite, quartz, and frag- 

 ments of schist or gneiss. About half-way from the height of land to 

 Swift river the rock is of much brighter colors, and contains mica, proba- 

 bly from fragments of gneiss. Below, there is a narrow band of a schis- 

 tose rock, that has itself somewhat the character of a sandstone, but so 

 jointed is it that it is difficult to determine the dip. This is succeeded 



