THK JUBA88IO SVSTKM 397 



:il'iiit half of thi.s l>elonging to the planorbe zone and the rest 

 to those of Schlotheimia anyulata and Coroniceras Bucklandi. 

 The quarries at Queen Camel and Street have yielded many fine 

 specimens of Ichthyosaurus, Plesiosaurus, fish, and other fossils, and 

 at the base are shaly limestones which contain remains of insects 

 and Decapod Crustacea (Eryon). 



Evidence that the higher /.ones persist is found in the occurrence 

 of the Ammonites semicostatus, obtusus, and oxynotus, but it is 

 doubtful if the Lower Lias in Somerset is more than 400 feet thick. 



Northwards, however, there is a rapid thinning, so that at 

 Shepton Mallet the same four xunes have a thickness of only 

 33 feet, overlain by 36 feet of clays and limestones referable to 

 the obtusum and oxynotum zones. Round the Mendip Hills there 

 are only irregular patches of limestone and clay to represent the 

 whole of the Lower Lias. To the north of the Mendips, however, 

 it soon regains its normal aspect and thickneas. 



Westward, in South Wales, there are fine exposures of the lower 

 beds in the cliffs between Penarth and Dunraven Castle. At 

 Penarth there is a normal sequence of Kinetic Beds with a thickness 

 of about 40 feet, and above them are the usual limestones and 

 shales for 135 feet, but when followed westward they exhibit a 

 remarkable lithological change. 



The Rhaetic Beds first pass into a massive oolite, and finally,, 

 near Bridgend and Pyle, into pale-green and yellow sandstones 

 with a medial band of green marls, shales, and limestones, the 

 whole being from 40 to 50 feet thick. The shales and limestones 

 of the overlying Lias pass westward into massive pale-coloured 

 marly limestones which overlap the Rhaetic sandstones so as to- 

 iv-t, with a conglomerate base, on the Carboniferous limestone at 

 Sutton and Brocastle near Bridgend. In these beds are corals of 

 the genera Astrocwnia, Montlivaltia, and Thecosmilia, together with 

 Pseudomonotis fallax and Ostrea liassica. Ammonites are scarce,, 

 but the higher beds contain Schlotheimia ungulata, Arietites 

 Bucklandi, and Arnioceras semicostatum. 



Middle Lias. On the Dorset coast this division is exposed in 

 the cliffs between Charmouth and Bridport, and presents the 

 following succession : 



Feet 

 Zone of Palt. ( Ferruginous limestone (marlstone) ... 1 



spinatum \ Yellow sands and sandy clays .... 77 

 /"Laminated micaceous sands and clays ... 72 

 Zone of Amal. | Blue micaceous clays with limestone nodules . 160 

 maryaritatus \ " Three tiers " of calcareous flagstone with 



V. sandy clays between 35 



