482 S. AUport — Rocks of Brazil Wood, Chamwood Forest. 



many other Charnwood rocks, has quite recently been admirably 

 described by Messrs. Hill and Bonney in a most valuable paper read 

 before the Geological Society ; 1 it will therefore suffice to give a 

 short account of two masses of granite and the altered sedimentary 

 rock. 



In Brazil Wood a small conical hill of granite rises about 70 

 or 80 feet above the surface, and is separated from the knoll of 

 " gneiss " by an interval of 35 yards ; this depression is occupied 

 by soil and vegetation, so that the junction of the two rocks cannot 

 be observed. On the occasion of our visit we found that recent 

 excavations had been made in the north-west corner of the quarry, 

 and had exposed to view a mass of granite which clearly forms 

 part of an intrusive vein. In one place there is a piece of the 

 gneiss completely inclosed in it, and it has thrown off smaller veins 

 which penetrate the gneiss in various directions. It will be seen, 

 then, that the beds of " gneiss " and slate are within 35 yards 

 (measured along the surface) of a considerable mass of granite, and 

 that they are also penetrated by granite veins ; they have been 

 subjected, therefore, to influences of the same kind which, in 

 Cornwall and elsewhere, have converted ordinary clay-slates into 

 crystalline micaceous schists. 



Hornblendic Granite, Brazil Wood. — The rock forming the conical 

 hill is a rather fine-grained granite of dark colour ; its constituents 

 are orthoclase, plagioclase, quartz, hornblende, biotite, magnetite, 

 and a few long slender prisms of a light brown colour not determined. 

 Although orthoclase predominates, the triclinic felspar is very abun- 

 dant, and occurs here and there in rather large crystals beautifully 

 striated. Both felspars are in a remarkably fresh state of preserva- 

 tion. Hornblende of a brownish-green colour is abundant, and is 

 frequently quite unaltered ; other crystals are however either partially 

 or completely altered to a green fibrous variety which closely 

 resembles uralitic pseudomorphs after augite. The Biotite is occa- 

 sionally quite unchanged, and exhibits its usual optical characters ; 

 much of it has, however, been altered to a pale green substance, 

 which is less strongly dichroic. The rock is a good one for the 

 study of this mineral, as it may be seen in every stage of alteration. 



Quartz is plentiful and contains many minute fluid cavities. 



Granite intrusive in schist. — This rock is also rather fine-grained, 

 but contains many crystals of white felspar, which give it a some- 

 what porphyritic character. The constituents are orthoclase, plagio- 

 clase, quartz, biotite. Both felspars are well preserved ; the orthoclase 

 exhibits many Carlsbad twins ; the plagioclase is comparatively clear, 

 and shows a very characteristic twin striation. The mica agrees in 

 every way with that described in the last-named rock. 



The Quartz is clear, but contains numerous very minute cavities 

 disposed in parallel lines ; it is worthy of remark that the direction 

 of these lines is the same in several adjacent grains of quartz. There 

 are a few small garnets near the junction with the schist, but none 

 have been observed at a greater distance than an inch. It is 

 1 Quart. Journ. Geol. Soc. 1877-78, vols, xxxiii. and xxxiv. 



