77 



The Norfolk varieties appear to t>e two: those of the Upper 

 Series and of the Lower, the former variety is a rather close- 

 grained rock, dark brown in colour, splitting along the bedding 

 planes into thin laminae, but with distinct planes of fracture. The 

 shale is highly elastic. The latter variety is a greenish-blue rock 

 less apt to split into thin laminae but prone to fracture into small 

 blocks. Both kinds of shale show an open texture, being more cr 

 less vesicular. When viewed under the microscope they are seen 

 to consist, in the main, of a yellowish resinous substance with, 

 in addition, narrow wedges of carbonaceous matter and lens- 

 shaped masses of a lighter-coloured organic substance. The 

 resinous substance which forms th© greater part of the bituminous 

 material of the Norfolk oil shale is composed of two distinct sub- 

 stances which differ in appearance, refractive indices, etc. Both 

 substances suggest a gelatinised scum- Inorganic grains occur, 

 mostly of silicates of alumina with iron, potash and water, such 

 as glauconite, which, however, is not so common as in the Dorset 

 oil shales. The Dorset oil shales show a general resemblance to 

 those of Norfolk, though according to Forbes-Leslie in the case 

 of the former the outline of the bedding planes is more distinct 

 and has a wavy contour with an almost entire absence of the 

 waxy material present in the Norfolk shales. The Dorset shales 

 have been more compressed than the Norfolk shales, possibly by 

 the mid-tertiary disturbances which caused the local Purbeck 

 Anticline and the wider Hampshire and London Synclines, and 

 Weald Anticline ; if not also by the cretaceous disturbances. (The 

 Norfolk Oil Shales. W. Forbes-Leslie, Bourn Inst. Petrol. Tech- 

 nologists. Vol. 3, No. 9 (1916), pp. 3-35.) 



Shale Mining and Recovery of Contents. 



m Shale mining is carried on in exactly the same manner as the 

 mining of coal. In the neighbourhood of Kimmeridge the shale 

 was won by means of adits driven into the hillsides or, as near 

 Clavell's Hard, into the cliff face, or of shafts sunk through the 

 unproductive beds. According to Mansel-Pleydell the process of 

 distillation was as follows : The retorts were charged with about 

 5cwt. of shale previously broken into pieces 2ins. square,' and the 

 temperature maintained as nearly uniform as possible. The crude 

 oil stood in tanks for 48 hours to let the ammonia-water subside, 

 and was then passed into a still. The first product was a light 

 oil, the second was a heavier oil containing paraffin. 



Mansel-Pleydell quotes a more detailed account by Dr. Ure 

 of the oily distillate. Various fractions were recognised. No. 1 

 was an offensively-smelting dark brown oil, suspended in a watery 

 liquid and charged with sulphuretted hvdrogen, ammonia and 

 carbon dioxide. No. 2, when purified by treatment with nitric 

 acid, which dissolved part, gave a light, colourless oil resembling 

 petroleum. The soluble part was largely composed of benzene 

 and possibly its homologues. The tar-like residue remaining after 



