46 ARCIL^AN. 



Messrs. Hill and Bonney, who at first were struck with the re- 

 semblance of some of the Charnwood slaty rocks to the Borrowdale 

 Series of Cumberland, now agree with Dr. Callaway and Dr. Hicks 

 in referring the series to the Pebidian group. ^ The Charnwood 

 rocks were long ago described by Sedgwick and Jukes, and later 

 on by the Rev. W. H. Coleman and Prof. Hull.^ 



At Whittle Hill are obtained the celebrated ' Charley Forest' oil 

 stones or Whittle Hill Hones. These are ground on the spot, and 

 are said to be among the best substitutes for Turkey oilstone. IMr. 

 W. J. Harrison describes the rock as a fine greenish-grey siliceous 

 slate. Slates are quarried for roofing purposes at Swithland. One 

 pit is 150 feet deep. The Groby slate pits are on the road leading 

 to Markfield : here the grain is not so fine as at Swithland. In 

 some instances the slate is of a purplish tint, with yellowish chloritic 

 veins running through it, in other cases it is of a dull greenish- 

 grey. The blue Groby slate has been used in the Albert Memorial, 

 Kensington Gardens.^ 



Devon and Cormvall. — The researches of Mr. J. H. Collins in the 

 Meneage Peninsula, and of Mr. A. R. Hunt along the coasts of 

 South Devon and Cornwall, have revealed evidence of the presence 

 in these areas of rocks which may be of Pre-Cambrian age. The 

 micaceous and chloritic schists of Bolt Head, Prawle Point, and 

 Start Point, in South Devon, are probably Arch^an ; and so also 

 may be some of the metamorphic rocks of the Lizard region in 

 Cornwall.* The Eddystone Lighthouse is built upon a reef of 

 gneiss, and the Shovel Reef, in Plymouth Sound, is in part gneissic ; 

 some of these rocks are massive, others more schistose, and they 

 appear to be of the old granitoid kind. Moreover, the horn- 

 blendic and other schistose rocks of Cornwall have been separated 

 by Mr. Collins from the Cambrian (Lower Silurian) rocks, and it 

 has been shown by Prof. Bonney that the latter are faulted against 

 the former.^ 



Gneisses also of a type which occurs in the lower part of the 

 Archsean series have been recognized in the Channel Islands by 

 Prof. Bonney and the Rev. E. Hill." 



1 Q. J. xxxi. 421. 



- Geology of Leicestershire Coal-field, etc. Nature, Nov. 23, etc. 1876. 



^ W. J. Harrison, vSketch of the Geology of Leicestershire, 1877. 



* T. G. Bonney, Q. J. xxxix. i; xl. I, Rep. Brit. Assoc, for 1885 ; and Address 

 to Geol. Soc. 1886, p. 85. 



^ H. Hicks, Proc. Geol. Assoc, vii. 73 ; J. H. Collins, Journ. R. Inst. 

 Cornwall, vii. ; and Trans. R. G. S. Cornwall, x. 47. 



'^ Q. J. xl. 404 ; xxxix. 24. 



