MESOZOIG TIME — TRIASSIC AND JURASSIC. 775 



They outcrop along the Apennines, the Pyrenees, and east-central Spain. 

 They cover large areas in central and northern Russia. The beds have a 

 small development along the Alps compared with the Triassic ; but the 

 fossils and rocks show, by their kinds, that the great continental sea was 

 here of unusual depth and purity. 



In Enaiand the subdivisions of the Jurassic series are as follows : — 



'■o^ 



1. Liassic Group. 



(1) The Lower Lias, consisting of clays, shales, and gray limestone, 

 and about 900 feet thick. 



(2) The Middle Lias, or Marlstone, a coarse shaly argillaceous and 

 ferruginous limestone with sand-beds and clays ; 200 to 350 feet thick. 



(3) The Upper Lias, consisting of clays and shales, and containing lime- 

 stone concretions ; 200 to 300 feet thick ; Avith the Midford sands in southern 

 England about 200 feet. The jet of the Yorkshire coast is a compact variety 

 of coal from the Upper Lias. 



These subdivisions were named in France by D'Orbigny : (1) the Sinemurian, from 

 the Latin word for the town of Semur ; (2) the Liassian ; and (3) the Toarcian, from 

 Thouars, in western France. 



2. Oolytic Group. 



(1) The Lower Oolyte. 



Divided into (1) the Inferior Oolyte, which includes the sandstones or Dogger of York- 

 shire and the Cheltenham beds — the Bajocian ; and (2) the Great or Bath Oolyte — the 

 BatJionian, including (a) the Fuller's earth, or clay-beds of varying thickness up to 400' 

 in Dorsetshire ; (6) the Stonesfield slate, a thin-bedded limestone in Oxfordshire, 

 and above it ; (c) the Forest Marble, consisting of sandy and clayey layers with Oolyte ; 

 and (d) the Cornbrash, a coarse shelly limestone. At Brora, on the east coast of northern 

 Scotland, there is a coal-bed 2 J' thick, overlaid by beds containing Middle Oolyte fossils. 

 In Yorkshire, the Inferior Oolyte contains estuarine beds with thin seams of coal and 

 many remains of plants. 



(2) The Middle, or Oxford Oolyte. 



Divided into (1) the Callovian, consisting of the Kellaways rock ; (2) the Oxfordian, 

 calcareous sandstone and the Oxford clay ; and (3) the Corallimi, made up of the Coral 

 rag or Coralline Oolyte, 10' to 120', with more or less of calcareous grit, 5' to 80'. 



(3) The Upper, or Portland Oolyte. 



Divided into (1) the Kimmeridgian, or Kimmeridge clay, having ferruginous con- 

 cretions in the lower division, called "doggers" ; (2) the Portlandian, or the Port- 

 land stone, including marlytes and limestone, in part oolytic, with fresh-water beds ; and 

 (3) the Furbeckian, or Purbeck beds, well displayed in Dorsetshire, mostly shales 

 with some limestone at middle which is partly of marine origin, 100' to 400' thick, and 

 affording remains of numerous Insects and Mammals. The "Portland dirt-bed" is at 

 its base. 



In Europe other subdivisions have been introduced, for which see 

 page 790. 



