LITIIOLOGY. 169 



Its feldspar is also labradorite, as shown by an analysis by Prof. Blanpied, 

 of Hanover (see p. 93). I have not found any hypersthene in it, and all 

 the constituents are in smaller crystals or grains. 



In going up the Mt. Washington river to observe this formation, one 

 is obliged to progress in the bed of the stream by springing from rock to 

 rock, since the woods are so thickly undergrown that they can with diffi- 

 culty be traversed. If one stops to look at the rocks on which he steps, 

 I think he will be struck with the variety of interesting specimens of 

 gabbro which have been brought down by the stream, and lie scattered 

 along its course. The stream in the spring time is a rushing torrent, and 

 rolls along large boulders. The region up this stream has not yet been 

 explored by a lithologist ; and I think that a careful search of it would 

 enable one to collect a scries of specimens of gabbro that would equal 

 in interest those from any one of the celebrated European localities. 

 Many water-courses and boulder-covered fields in New Hampshire pre- 

 sent a most diversified cabinet of lithological specimens, but which lose 

 their present value because their origin and surroundings are unknown. 

 Many may have travelled long distances, and many may be in place near 

 by; but the observation of these boulders is of interest to the student 

 as indicating the possibilities of our future lithology. 



There are two or three kinds of boulders which ought not to be en- 

 tirely passed by, because they have attracted much attention and are 

 widely known, and they may naturally be mentioned here. In and about 

 Gilford are many boulders of a beautiful variety of gabbro, in which the 

 large, foliated grains of diallage are round in form, and spot the rock in 

 such a way as to make it very beautiful. Thin sections under the micro- 

 scope show that this diallage is partially altered to hornblende. A chem- 

 ical examination indicates that the feldspar is anorthite. Our country^ 

 which has furnished thus far few gabbros, certainly possesses a most in- 

 teresting and beautiful one, which this represents. 



The labradorite boulders in Stark are very well known, and many peo- 

 ple have taken specimens from them. Though found in no other place, 

 they are there so abundant that some have thought they must be in place 

 near by. I have some thin sections cut from these rocks. They are es- 

 sentially composed of labradorite. The interspaces between the crystals 

 of this mineral in most of the rocks are filled with hornblende, biotite, 

 VOL. IV. 22 



