52 



THE DIVISION OF 



The clays of the Upper Lias forming the lower part of the zone, are everywhere distin- 

 guished by other species of Falciferi, as Ammonites bifrons, Brug. ; A. serpentinus, Schloth., 

 and numbers of the group Planulati, as Ammonites communis. Sow. ; A. anguinus. Rein., 

 and A. Jibulatus, Sow. 



The Middle Lias. — This is divisible into five zones, each characterised in descending 

 order by — Ammonites spinatus, Brug. 2. A. margaritatus, Mont. 3. A. capricornus, 

 Schloth. 4. A. Ibex, Quenst. 5. A. Jamesoni, Sow, 



The Lower Lias is divisible into seven zones. These are — 1. Zone of A.raricostatus, 

 Ziet. 2. A.oxynotu8,^\\&Ti%i. 3. A.obtusus, Sow. 4. A. Turneri, Sow. 5, A.Buchlandi, 

 Sow. 6. A. angulatus, Schloth. 7. A. jjlanorbis, Sow. 



Complicated as these subdivisions may at first sight appear to those who have regarded 

 the Lias merely as a great clay deposit, with a uniform fauna throughout, still theii' 

 accuracy may be clearly demonstrated in the grand section on the Dorsetshire coast, 

 extending from near Bridport harbour on the east, to Pinhay bay on the west. Within 

 these limits the entire series of beds rise beneath each other on the shore, and are exposed 

 in the cliffs, so that this coast section may be said to be complete from the great arenaceous 

 deposit of Upper Lias sand, containing Ammonites opalinus, with each succeeding zone of 

 the Upper, Middle, and Lower Lias, down to Ammoiiites planorbis, and its Ostrea series 

 resting on the Avicula contorta beds of the Trias formation. 



In the following table I have placed the different zones of the English Lias in corre- 

 lation with those of Germany, so well described by Professors Quenstedt, Oppel, Fraas, and 

 others ; those of France by the late M. A. d'Orbigny, and of those of England by 

 Sir R. Murchison, Sir H. De la Beche, and the Rev. W. D. Conybeare. 



