JURASSIC PERIOD. 435 



The promiment subdivisions of the Jurassic formation observed in England (though 

 not present alike in all its Jurassic regions) are the following, beginning below: — 

 I. Lias. 



1. Lower Lias : consisting of grayish laminated limestone, with shale above. 



2. Middle Lias : a coarse shell}' limestone, called maris tone. 



3. Upper Lias: beds of clay or shale, with some thin limestone layers. 



II. OOLYTE. 



1. Lower or Bath Oolyte, consisting of — 



(1.) Inferior Oolyte, & limestone with fossils and layers of sand. 



(2. ) Fuller' s-ewrth group, or clayey layers. 



(3.) Great Oocyte, limestone, mostly oolitic. 



(4.) Forest-marble group, sandy and clayey layers, with some oolite. 



(5.) Cornbrash, a coarse shelly limestone. 

 The Stonesfield slates, noted for their remains of Saurians, as well as of the earliest 

 British Mammals, and also of Insects and other species, occur near Oxford in England, 

 and belong to the Lower Oolyte, below the Great Oolyte. 



At Brora, in Sutherlandshire, there is a bed of Oulytic coal of good quality, three and 

 a half feet thick, which has been long worked: it is covered by several feet more of 

 impure coal, containing pyrite. It is supposed to belong with the Great Oolyte. 



2. Middle or Oxford Oolyte: consisting of — 



(1.) Kelloway Rock, a calcareous grit, overlying blue clay, and overlaid 



by (2.) the Oxford clay. • 



(3.) Calcareous grit and oolitic coral limestone, called the Coral Rag. 



3. Upper or Portland Oolyte : consisting of — 



(1.) Kimmei-idge Clay. 



(2.) Shotover Sand, a calcareous rock with concretions. 



(3.) Portland Oolyte. 



4. Purbeclc beds: consisting of (1) the Lower Purbeck, fresh-water marls, with 

 the "Portland dirt-bed," and resting on the upper layers of the "Portland 

 stone;" (2) the Middle Purbeck, mostly a bed of marine limestone, 30 feet 

 thick; (3) the Upper Purbeck, 50 feet of fresh-water deposits. The dirt-bed 

 of the Purbeck is the second deposit affording remains of British Mammals. 

 It contains also numerous remains of Cycads, etc. 



III. Wealdem. 



1. Hastings Sands: sandstone, with some clayey and limestone layers, containing 

 Saurian remains, fluviatile shells, etc. 



2. Weald Clay : clayey layers, with some calcareous beds containing fresh-water 

 shells. 



The British subdivisions are for the most part recognized in France, and have re- 

 ceived special names from D'Orbigny. They are (I. ) in the Lias, — 1, the Sinemurian 

 (Lower Lias, named from the locality at Se'mur); 2, Liasian (Middle Lias); 3, Toarcian 

 (from the locality at Thours); (II.) in theOoLYTE, — 1, Bajocian (the inferior part of 

 the Lower Oolyte, named from the locality at Bayeux); 2, Bathonian (the GreatOolyte, 

 Bath Oolyte): 3, Callovian (Kelloway Rock); 4, Oxfordian (Oxford Clay); 5, Corallian 

 (Coral Rag); 6, Kimmeridgian (Kimmeridge Clay); 7, Portlandian (Portland Oolyte). 

 In the French Juras, the Lias limestone is called also Gryphite limestone, from the 

 abundance of the fossil Gryphcea incurva. 



For the '"Inferior Oolyte" Marcou has used the name Lmdonian; for the Fuller's 

 earth, Vesulian. Thurman and Etallon have restricted Corallian to the lower part of 

 the Corallian of D'Orbigny (the part called Rauracian by Creppin), and named the 

 upper part, commencing with the beds containing Astarte minima and including the 

 lower part of the Kimmeridge clay, the Astartian (the same is the Sequanian of M. 

 Jourdy) ; the Kimmeridgian, comprising the middle part of the Kimmeridge Clay, is 

 the Strombian of Thurmann. The Portland Oolyte is the Portlandian of Marcou (or 

 Virgulian of Thurmann) ; and, lastly, the Purbeckian is the Dublisian of Desor and 

 Tithonic of Oppel. The Wealden is Lower Neocomian of D'Orbigny. 



