80 RET. EDWIN HILL AND PROF. T. G. EONNEY OjST THE 



the one side, through the plantations of Strawberry Hill and Cat 

 Hill on the other, and from Abbot's Oak, skirting Timberwood Hill, 

 across these two. These boundaries are probably natural ones, for 

 they follow the features of the ground, and do not leave any out- 

 crops outside, though many come close to or are upon them. 



The first line is parallel to the well-marked horizon of the Elack- 

 brook Group, and the second (about a mile from the first) only 

 makes an angle of 7° with that horizon. The third, if produced, 

 also skirts the slopes of Bard on Hill and suggests a fault. The 

 boundary of visible rock in the remaining direction (N.W.) is 

 irregular. The rocks within these limits have few representatives in 

 the rest of the Forest. The outcrops from the S.E. boundary up to 

 Peldar Tor and Sharpley are, in general, confused heaps of agglo- 

 merate, and ashes without large fragments are rarely seen. Then 

 come the areas occupied by the porphyroids of Peldar Tor and 

 Sharpley which are in contact along a very short line (from Abbey 

 Grange to Spring Hill Farm, about a quarter of a mile). The 

 remainder of the region also contains agglomerates and ashes, the 

 latter, without conspicuous fragments, being more frequent than in 

 the southern part ; yet even here the majority of outcrops are 

 agglomerates. Even the very flinty slate at the Car-Hill Quarry^ 

 Whitwick, and at that near the Forest-E,ock Hotel do not indicate 

 thick masses, and are seen to pass into beds of ashy materials. 



2. The Porphyroid of Peldar Tor. — We have little to add to 

 or correct in our published description of the general macroscopic 

 characters of this rock. The dull green colour of the matrix, the 

 rough external surface, the rugged and almost lumpy weathering 

 are features markedly characteristic. We have observed, howevePy 

 that some of the outcrops on the western margin of the mass 

 approach the Sharpley type in that they display a smoother surface 

 and a tendency to bleach in weathering. Included fragments are 

 not numerous, and are generally small, though occasionally a 

 fragment several inches in diameter may be found *. Some resemble 

 the porphyritic felstone which is common in the neighbouring' 

 volcanic breccias ; others (the more numerous) are a rather fine- 

 grained reddish-grey rock. The Peldar porphyroid, here and there, 



* The largest which we observed was 18" in diameter — an exceptional size. 

 This specimen under the microscope exhibits a groundmass consisting of nume- 

 rous small felspar crystals — often about "02" long — some with Carlsbad twinning 

 and resembling orthoclase, some plagioclase. The intervals are blackened with 

 opacite or occupied by viridite. We find also grains of epidote and of iron 

 oxide (? ilmenite more or less altered). In this groundmass are one or two 

 small grains of quartz and several larger crystals of felspar, some showing 

 plagioclastic twinning. All exhibit a rather rounded central part speckled with 

 cjpacite, surrounded by a clearer margin, which has a more rectilinear boundary. 

 A slide from a compact-looking fragment, collected from the S. side, much 

 resembles in general character the rock of the " pmqjle porphyritic " fragments at 

 E-atchet Hill, &c., though the quartzes and felspars are smaller, and its ground- 

 mass puts on occasionally the slightly "granular" aspect characteristic of the 

 ordinary Peldar rock. Now and then these " granules " give indications of 

 spherulitic structure. There is a nest of small felspar crystals and epidote (?)y 

 an inclusion from a yet older rock. 



