UPPER LIAS. 279 



been known since early British times, having at first been picked 

 up on the sea-shore at Whitby and other places. It is now 

 mined both in the cliff and inland. The largest seam of jet on 

 record was obtained from the North Bats, near Whitby ; it weighed 

 370 stone and was worth about £zz^o} Jet is one of the most 

 valuable products of the Yorkshire coast, being extensively worked 

 into ornaments. It is a resinous variety of lignite, and Prof. 

 Phillips observes that it is simply coniferous wood, and in thin 

 sections it clearly shows the characteristic structure. Impressions 

 of Ammonites and other fossils sometimes appear on its surface. 



The Alum Shale consists of hard blue shale with cement-stones. 

 On exposure to the air the shale gradually becomes incrusted with 

 sulphur, and occasionally with alum. The nodules are most abun- 

 dant in the upper part, below comes the main mass of Alum Shale 

 in which Leda oviwi is abundant, the shales at the base are unpro- 

 ductive of alum. The remains of Reptiles, Plesiosaunis, Ichthyo- 

 saurus, and Teleosaurus are more abundant in the Alum Shale than 

 in the lower divisions of the Lias. Belemnites and Ammonites are 

 likwise abundant; among the species are B. vulgaris, B. IcBvis, A. 

 communis, A. bifrons, A. heterophyllus, etc. Trigonia literala and 

 Discina 7-eflexa also occur. In composition the Alum Shale is as 

 follows : — 



Iron sulphide 8-50 



Silica 5i'i6 



Iron protoxide 6'ii 



Alumina 18 30 



Lime 2' 15 



Magnesia '90 



Sulphuric acid 2*50 



Potash trace 



Soda trace 



Carbon 8-29 



Water 200 



99-91 



From this shale potash-alum was formerly made near Whitby and Redcar: the 

 aluminium sulphate being extracted from the shale, and the potash-salt being 

 added. The trade, which since the days of Queen Elizabeth has been largely 

 carried on, has now almost passed away, as alum is now manufactured in other 

 places from Coal-shale. Alum works formerly existed at the Peak, Robin Hood's 

 Bay, Stow Brow, Sandsend, Kettleness, Lofthouse (Loftus), Osmotherly, etc. 



At Whitby good hydraulic cement (Mulgrave cement) has been made from 

 the nodules in the Alum-shale. The Upper Lias clay is frequently used for 

 making bricks, tiles and drain pipes. 



1 Tate and Blake, Yorkshire Lias, pp. 17S, 188. 



