TIIK .H'KASSIC SYSTEM 405 



rop being interrupted only in the north-east where they are 

 concealed beneath the overstepping Cretaceous deposits between the 

 Ardennes and the Boulonnais. It is unnecessary to burden the 

 student with details of the local variations exhibited by the Lias 

 in this and other parts of France, and it will suffice to give a brief 

 account of its development on the eastern borders of the country 

 in Alsace, Lorraine, and the Jura district, while the very different 

 facies found in Provence will be referred to under the head of the 

 Alpine region. 



French geologists divide the Liassic Series into five stages, making 

 the Rhaetic one of them, but as it has really only the value of a 

 zone it is better to include it in the overlying stage (Hettangian). 

 If this is done we have the following stages in descending order : 



4. Toardan. Zones ofjurense, commune, and falciferum. 



3. Charmouthian. Zones of spinatum, maryaritatus, capricornus, 



and armatum, 

 2. Sinemurian. Zones of raricoslatum, obtusum, Turneri, and Buck- 



landi. 

 1. Hettangian. Zones of angulata, planorbe, and Pteria contorta. 



The French also include the zone of Lioceras opalinum in 

 their Toarcian, but the Germans do not, and in England its equi- 

 valent is usually regarded as the base of the Inferior Oolite. 



How far the Hettangian zones extend under the Paris basin is 

 unknown, but probably all the higher stages are continuous beneath 

 that basin and the English Channel, passing into their equivalents 

 in the south of England. The Upper Lias has recently been 

 reached by a deep boring at Rouen. 



Hettangian. This takes its name from Hettange in the south 

 of Luxemburg, in which district this part of the series has an 

 unusual thickness because it consists largely of estuarine beds, 

 as below : 



Feet 



y . /Sandstone with marine shells and plant remains . 200 



las \Blackclaysandblacklimestones ... .30 



,. /Red clays with one or more bone beds . . .18 



' \Yellow micaceous sandstones . . . . 25 to 30 



The black beds contain few fossils, but must represent the zone 

 of Psiloceras planorbe, and the Hettange sandstone that of Schlo- 

 theimia angulata. In Alsace and Lorraine the Rhaetic presents a 

 similar facies and maintains a thickness of from 30 to 40 feet, but 

 both the zones of Psiloceras planorbe and Schlotheimia angulata 

 are so thin as to be scarcely recognisable. 



Sinemurian. In the north-east of France this stage consists 

 principally of grey limestones in regular beds full of Gryph&a arcuata, 



