310 



Scientific Geology. 



of these crystals are one or even two inches in diameter ; though in 

 such cases generally imperfect. Often this mineral is compact, and 

 the color either white or lilac red. This red color, however, occurs 

 also in that which exhibits an aggregation of prisms. Bolton and 

 Boxborough yield an abundance of this beautiful variety. 



It is probable that the mineral from Bolton described by Mr. 

 Brooke, under the name of Nuttallite, is only a variety of scapolite. 



Augite, actynolite, pargasite, and radiated, fibrous, and brown horn- 

 blende, are among the minerals found in this limestone; the two first 

 at all the localities, the third at Carlisle and Boxborough ; and the 

 fourth, according to Mr. Nuttall, at Bolton. 



Phosphate of lime, sometimes in hexahedral crystals, but more 

 commonly massive, is found at Bolton, Boxborough, and Littleton ; 

 usually in scapolite. Its colors are green and purple. 



Spinelle, dark green and grayish blue, occurs at Bolton, Boxbor- 

 ough, and Acton, both massive and in regular octahedra. Some of 

 the specimens at Boxborough, incline to rose red; and in the opinion 

 of Mr. Nuttall, are the genuine spinelle ruby. 



Genuine petalite, (from which lithia has been obtained,) exists at 

 the south quarry at Bolton, associated with the scapolite. 



At Chelmsford small masses of black serpentine occur in the lime- 

 stone, and at Littleton of a lively green colour. 



At Carlisle, close by the turnpike from Concord to Groton, Prof. 

 Webster discovered a few years since, a splendid garnet, which is 

 probably a cinnamon stone. The specimens which can now be ob- 

 tained, give but a poor idea of the richness of some of those which 

 were first procured. Probably extensive exploration might bring to 

 light finer specimens. The same mineral is found at Boxborough. 



At Bolton rhomb spar occurs: and both there and at Boxborough, 

 a beautiful variety of flesh colored calcareous spar in foliated masses. 



At Bolton, also, a new mineral has been discovered, which Dr. 

 Thomson has denominated from its chemical composition, Bisilicate 

 of Magnesia; and Mr. Shepard, with reference to its locality, calls it 

 Boltonite* It occurs in foliated masses in the limestone. (Nos. 521, 

 522.) 



In the same place, sphene, or silico-calcareous oxide of titanium is 

 not an uncommon mineral at the south quarry — in distinct crystals. 

 Tremolite, also, is said to occur there in fibrous masses : also gado- 



* Shepard's Mineralogy, Vol. 1. p. 232. 



