TIIK JUltASSIC SYSTEM 



Lower Lias. The succession of beds which constitute the 

 Lower Lias at Lyine Regis is as follows in descending order : -' 



Green Ammonite 

 Beds 



Feet. 



I Bluish - grey marly clays with Rhacoceras\ 

 Loscombei 



- 105 



\Bluisli-grey marly clays with I'fut >/j>/' nroceras j 

 latcKCosta J 



i I Tale-grey marls with some marly limestones ; 



Belemmte Beds | few B fo * 8il8 . . . . ... 80 



fShaly marls with Echioceras raricostatum . . 15 



Ml V SV> 1 ' Shaly niarls with OsijMt-iceras oxynotum . . 15 

 ~| Dark-grey shalesand limestones with Astcroccms 



\. obtusuni and Asteroceras Brookei . . . 170 



/ Shales and marls with Arnioceras semicostatum 18 

 p, T . | Limestones and shaly clays with Coroniceras 



1 Biicklandi and Schlotheimia awjulata . . 67 



V. Limestones and shales with Psiloceras planorbe 20 



j " \Viiite Lias," limestones, and shales . . 25 



Rhsetic Beds -! Black shales with Pteria contorta ... 32 



I Grey marls and limestones (passage-beds; . 30 



577 



The Rhsetic Beds are exposed to the west of Lyme Regis at 

 Charton Bay and Culverhole (see Fig. 131). Throughout Dorset and 

 Somerset there are a set of passage-beds between the Keuper marls 

 and the Rhsetic Beds, and these have recently been called the Sully 

 Beds by Mr. L. Richardson. 3 The base of the Pteria contorta zone 

 is marked by a layer of calcareous grit full of the bones and 

 coprolites of fish and small reptiles ; this is also of general 

 occurrence, and is known as " the bone bed." In the White Lias 

 or Upper Rhoetic Ostrea liassica and Modiola minima are the 

 commonest fossils. 



The succession of zones and sub-zones is normal up to that of Ech. 

 raricostatus, but above that the typical Ammonites are rare. The 

 Belemnite Beds are supposed to represent the armatum, Jamesoni, 

 and ibex zones, but the two latter species of Ammonites do not 

 occur. The succeeding beds may be regarded as the equivalent of 

 the zone of Atgoceras capricornus, and its sub-zone of JEg. Henleyi. 



In Somerset the beds forming the Lower Lias are similar to 

 those of the Dorset coast, but the higher zones are seldom exposed. 

 Near Watchet on the Bristol Channel there is a good section of 

 Rhaetic Beds (Black Shales and White Lias, 46 feet) and of Lower 

 Lias for about 150 feet, including the planorbe, angulatum, Buck- 

 landi, and semicostatum zones. 



The limestones of these lower zones have been quarried at many 

 places from Ilmintstur eastward, and are upwards of 200 feet thick, 



