04 KEV. EDWIN HILL AND PROF. T. G. BONNEY ON THE 



nearly -1 inch in diameter, and the flakes of mica (especially of ther 

 white) sometimes about half this length ; but the structure of this 

 part of the altered rock and of the granite has been so admirably 

 described by Mr. S. Allport that it is needless to do more than refer 

 to his paper *. 



It is then evident (as stated in our last paper) that the name- 

 " gneiss," by which this rock was formerly designated, must be 

 dropped, and, until petrographers agree upon a nomenclature for the 

 products of contact-metamorphiam, we may designate it simply " a 

 micaceous rock," for it cannot properly be named a schist. Its- 

 slickensided condition, so often noticed, the development in the 

 garnets of cracks and a rude cleavage, and of the latter in parts of 

 the rock, indicate that the intrusion of the granite was prior to the' 

 chief earth-movements "which have affected the Forest. We did 

 not succeed in finding (but in such a place it might easily be 

 overlooked) any outcrop of sedimentary rock at a greater distance- 

 from this pit. We are, however, disposed to conjecture that the latter 

 originally consisted of materials generally similar to those of the 

 slaty series at Swithland and Groby. 



9. The BlackhrooTc G^^oujj). — Aided by the six-inch map we have 

 found several outcrops previously unknown to us. A long narrow 

 plantation N.E. of Gun Hill, called Strawberry Hill, covers a sort of 

 ridge, in the middle and at the southern end of which rock may 

 be seen ; the materials are ash with fragments. A wood called 

 Cat Hill, N.E. of Timber wood Hill, surrounds a steep crest of ashy 

 rock. On the line between these two lie the long narrow ridge of 

 Collier's Hill (in the grounds of Charnwood Lodge) and the crags- 

 of the Hanging Stones (Flat Hills). These last contain many 

 fragments. We thiuk our specimens from these localities show 

 some common features ; accordingly we regard this group of out-^ 

 crops as a base to the vast mass of agglomerates which occupy the- 

 area of the North-west region. Their line is parallel to another 

 which may be drawn through the outcrops of the Blackbrook ToUgate- 

 (Einging Hill), the old reservoir (Blackbrook Yalley), the Oaks 

 Church, and Mr. Dexter 's Farm (north of Charley Hall), on which 

 also lies an outcrop north of the railway, altogether a line four miles 

 long. The rocks along the latter line are characteristic examples- 

 of what we have called the Blackbrook Group, being entirely 

 unlike those of the North-west region ; though the}' consist mainly 

 of volcanic materials, the constituents are much smaller in size, and 

 of a felsitic nature. 



A small quarry, previously unnoticed, in a field east of Charley 

 Mill, contains rock which is of typical Blackbrook character, but it 

 lies half a mile S.W. of this line, and must be displaced by a fault.- 

 As, moreover, the rock near White Horse Wood (300 yards west of 

 the White Horse public-house) is indistinguishable from that of the 

 pits at Blackbrook Tollgate (Ringing Hill), but is half a mile N.E^ 

 of the line of strike, it is probably the same repeated by another 

 fault. 



* Geol Mag. dec. ii. vol. vi, (1879) p. 481. 



