TIIK JUKASSIC SYSTKM 



401 



base of this, so that the restricted Upper Lias would consist of 

 the following : 



Leda Ovum Beds (zone of Am. Lilli) 



Cerithium Beds (Cerithium armatum) 



Zone of Dactylioceras fibulatum and Hildoceras bifrons 

 ,, Dactylioceras subcarinatum (Commune Beds) 

 , ; Harpoceras falcifcrum (Serpentinum Beds) . 

 ,, Am. lateseens (Fish Beds) .... 



Feet. 



36 



36 



76 



5 



4 



2 



159 



A similar set of beds is found in Rutland, but in Lincolnshire 

 the highest beds seem to have suffered erosion before the deposition 

 of the overlying sandstone, and the highest remaining part of the 

 Lias belongs to the bifrons zone. On the other hand the 

 serpentinum Beds thicken northward to about 40 feet, and the 

 total thickness of the stage at Lincoln is about 100 feet. 



3. Yorkshire 



In the south of Yorkshire, from Brough to Kirby Underdale 

 and Howsham, the Lias is similar in all respects to that of North 

 Lincoln, but as soon as the valley of the Derwent is crossed a 

 change begins to be manifest, both the Middle and Upper Lias 

 swelling out till they again attain a development equal to that of 

 South Lincolnshire. From Howsham the outcrop curves round by 

 Thirsk and Northallerton to the coast between Redcar and Whitby, 

 which exhibits an excellent section of the whole formation except 

 the zone of Psiloceras planorbe. 



The following is a rdsume of the coast section : " 



Upper, 



Middle, 

 140 feet 



Blea Wyke sauds with Harpoceras aalensis, 50 feet. 



Blue shales, with Harp, striatulum and H. variabilis, 70 



feet. 

 "Alum shales" with Dactylioceras commune, Hildoceras 



bifrons, and Leda ovum, 90 feet. 

 Blue shales with calcareous doggers and layers of jet in the 



lower part. Harpoceras serpentinum, Belemnites tubu- 



laris, Inoceramus dubius, 90 feet. 

 Grey shales with Dactylioceras annulatum and Belemnites 



cylindricus, 30 feet. 

 Ironstone (Cleveland main seam) and shales below, zone 



of A maltheus spinatus, 30-50 feet. 

 Ironstone (lower seam) or Pecten Bed, with beds of marly 



sandstone below ; contains Amaltheus margaritatus and 



Pecten laevis, about 100 feet. 



2D 



