394 



DK. W. HIND AND MR. J. A. HOWE ON THE [Aug. IQOI. 



undertaken for us by Mr. E. F. Eobinson, will assist in conveying 

 an impression of the nature of the rocks under discussion. 





~~5 



t 

 3U 



2^8 



3L3 



3LB 



it 



226 



t 

 316 



t 

 319 



227 



* 

 187 











CaO 



per 



cent. 



42-51 

 2-62 



38-94 

 5-09 

 4-15 

 1-10 

 4-48 

 0-27 



per 

 cent. 

 40-09 

 1-11 

 31-96 

 17-57 



\ 5-38 



3-16 



o-ii 



per per | per 

 cent. cent. cent. 

 13-80 i 46-80 20-23 

 0-71 1 0-15 ' 0-20 

 11-19 36-75 ' 16-50 



per 



cent. 



48-37 

 0-14 



38-20 

 9-32 



trace 

 2-25 

 107 

 0-11 



per 

 cent. 

 34-28 

 trace 

 31-24 

 24-00 



|- 8-22 



1-90 

 0-54 



per 

 cent. 



42-84 



0-59 



36-69 



13-37 



4-57 



1-59 

 0-15 



per 

 cent. 

 54 -.53 



o-u 



43-08 

 0-61 



trace 

 0-56 

 0-34 

 0-18 



per 



cent. 

 .52-80 

 trace 

 41-67 

 0-55 



|- 3-65 



0-44 

 0-15 



99-26 



MffO 



COo 



SiO'2 & insoluble residue. 

 FeO 



54-03 



8-45 



10-45 

 0-68 



9-16 54-33 



AI0O3 



3-36 



3-76 

 0-11 



4-»4 



2-88 

 0-51 











99-16 



99-38 



99-31 ! 100-09 99-49 99-46 



1 1 



100-18 



99-80 



99-41 



* These rocks are from the ' Knoll Limestone.' t From Pendle Hill, tt A local phase 

 of the Mountain Limestone. All the others are from the Pendleside Group. 



225. A black limestone, from shales in the valley of the River Dane (North StaflFord- 



shire). 

 31k. Dark limestone, from shales in stream at Hall Foot House, Worston (Lancashire). 

 228. Black, soft limestone, from shales at Cromford (Derbyshire). 

 3lt3. Black limestone, from near the base of Btebden Hill (near Cracoe). 

 3lt6. Muddy limestone, from shale at the south-eastern corner of the foot of Keal Hill, 



Thorpe (near Grassington). 



226. 'Black Marble,' from Ashford (Derbyshire). 



316. Hard, grey, siliceous limestone, from Pendle Hill (Lancashire). 

 219. Brownish limestone, with sponges, from Pendle Hill. 



227. White limestone, from Hill Bolton, near Grassington. 



187. White limestone, from Bunster Hill, Dove Dale (Staffordshire). 



The first five rocks in the foregoing table are all black rocks, 

 varying considerably in hardness and texture ; the two hardest 

 (IS^os. 225 & 343) have a higher percentage of lime than the others, 

 while the two softest (Nos. 228 «fe 346) yield the highest propor!"'ion 

 of insoluble residue. 



As might be expected, the amount of organic matter is higher 

 in these black rocks than in any of the others, but varies both in 

 its amount and nature. In I^o. 228 there is a good deal of volatile 

 hydrocarbon present : this may be distilled off at a low temperature, 

 leaving behind some bituminous substance which is expelled at a 

 higher temperature. This rock is only a hardened phase of the 

 black shales in which it occurs, and approaches an oil-shale in 

 character. 



All these black rocks exhibit in section minute fragments of 

 vegetable origin, scattered throughout the mass, or lying along 

 lines parallel to the stratification. Their dark colour is due in part 

 to the presence of these vegetable fragments, but in addition, the 

 granular calcite of which they are mainly composed is uniformly 

 stained, the thin sections appearing yellow or brown, or being 

 quite opaque and black. 



Iron (in the condition of sulphide and oxides) is invariably 

 present, and no doubt assists in the colouring of the rock, but it 

 is interesting to note how small a percentage of either iron or 

 carbonaceous matter is effective in producing the dark colour, for in 



