244 ROCKS OF BRAZIL WOOD, CHARNWOOD FOREST. 
quarry, is a dyke of diorite, first noted by the Messrs. Hill and Bonney. 
(‘‘ Quarterly Journal of Geological Society,” Vol. XXXTYV., p. 223.) 
The rock forming the conical hill has the same mineral constitution 
as that of the larger granitic masses above mentioned, although it differs 
from them in appearance. It is a rather fine-grained hornblendic 
granite, having all the constituents well crystallised, and in a remarkably 
fresh state of preservation. It may ke regarded as a good typical 
example of this variety of granite, and forms a very beautiful prepara- 
tion for the microscope. 
The so-called gneiss is almost wanting in two of the essential 
characters of that rock; it contains scarcely a trace of felspar, 
and the foliation is very imperfect. The only recognisable minerals 
are mica and quartz, and as the mass of the rock is rather fissile 
in one direction, it might be called a micaceous schist, in 
order to distinguish it from the typical mica schists, from which it 
differs in some respects. These rocks will be more fully described 
hereafter. 
The knoll of “gneiss” is separated from the granite by an interval 
of 35 yards, and this depression is occupied by soil and vegetation, so 
that the main junction of the two great masses of igneous and aqueous 
rock cannot be observed. Masses of a dioritic rock have been found on 
the surface of this interval or passage both by ourselves and Messrs. 
Hill and Bonney, and the relation of the three sets of rock (viz., the 
granite, ‘‘ gneiss,” and diorite) to each other has hitherto been a matter 
on which nothing certain was known. 
By observations recently made we are enabled to prove that the 
granite is clearly intrusive in the “gneiss,” and that the latter rock is 
probably the result of the alteration of clay-slates belonging to the 
Forest series. 
An opening has been made in the “ gneiss;” it has been worked 
back 25 yards from the edge nearest the granite, soas to expose a “face” 
50ft. in width and 33ft. in height. It is worked for road metal for the 
immediate vicinity, and a large heap of broken stone usually lies on the 
floor of the quarry. Onthe “face” the remarkable contortions of the 
rock at once attract attention, those in the south-west corner being very 
abrupt and “diagrammatic.” The mass of the stone is of a dark- 
purplish hue; the broken surfaces glitter with flakes of mica; it is 
excessively tough and much jointed, the joints being frequently curved 
and showing marks of slickensides. 
In the north-west corner of the quarry (where excavations have 
recently been made) we noted a rock of very different character to 
the ‘‘gneiss” above described. Here, underneath a tree, whose roots 
penetrated its yielding substance, we found a mass of decomposed 
granite, 5ft. in width. As this passes downwards it sends off narrower 
veins into the gneiss, which reach nearly to the floor of the quarry; but 
the main granitic vein turns southwards and enters the face of the quarry, 
enclosing here a lenticular piece of the metamorphic rock, which measured 
a 
