180 GEOLOGICAL HISTORY. 



Gasteropoda. Annulosa. 



Cephalo|K>da. Fishes. 



Crustacea. Enaliosauria. 



Of freshwater animals and plants, we have perhaps none in 

 the Lias ; but terrestrial plants are represented by fragments of 

 coniferous trees of considerable magnitude, often converted to 

 brilliant jet. 



MEOALOSAURIAN PERIOD. The depression of the sea-bed 

 during the period which succeeded the Lias must have been 

 subject to several interruptions and renewals. For in this series, 

 as it appears in Yorkshire, we have several alternations of oolite, 

 the produce of salts dissolved in the sea-water; shales widely 

 diffused in that water ; sandstones full of false bedding, indicative 

 of shallow and variable currents; ironstone and beds of coal, 

 which imply not far distant land. Swampy land, if not river 

 channels bearing fresh water, we may perhaps readily admit even 

 in the very area of Yorkshire, for stems of Equiseta stand up- 

 right in certain sandstones near Whitby and Osmotherley*, like 

 the Sigillarise and Lepidodendra of the older deposits, and like 

 them are associated with coal. But we cannot from this occur- 

 rence, or from the bones of land lizards (Megalosaurus) in the 

 Coralline Oolite, conclude that there was elevated land in the 

 region where now the North York Moors rise 1485 feet above 

 the sea. 



Marine plants are but slightly traced in any of the strata of 

 this period in Yorkshire, but marine animals abound in all the 

 limestones, and many of the sandstones and clays. The follow- 

 ing are the main groups : 



Amorphozoa. Dimyaria. 



Polyparia. Monomyaria. 



Foraminifera. Brachiopoda. 



Asterida. Gasteropoda. 



Echinida. Cephalopoda. 



Crinoidea. Crustacea. 



* Their observation at Osmotherley is due to Murchison. 



