3 THE LIAS AMMONITES. 



H. insigne, Schiibl., with Lytoceras jurense, Ziet., L. Jdrcinum, Schliib. The clays 

 forming the lower part of the zone are everywhere distinguished by Harpoceras 

 bifrons, Brug., H. serpentinum, Schloth., and numbers of the group Stephanoceras, as 

 Steph. commune, Sow., S. anguinum. Rein., and S.Jibulatum, Sow. 



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

 ing order by — 1. Amaltheus spinatus, Brug. 2. A. margaritatus, Mont. 3. Aegoceras 

 Henleyi, Sow. 4. Amaltheus Ibex, Quenst. 5. Aegoceras Jamesoni, Sow. 



The Lower Lias is divisible into seven zones. These are — 1. Zone of Arietites 

 raricostatus, Ziet. 2. Amaltheus oxgnotus, Quenst. 3. Arietites obtusus. Sow. 4. A. 

 Turneri, Sovf^. b. A. £ucMandi,Sow. 6. Aegoceras angulatiim, Schloth. 7. Aegoceras 

 planorbis. Sow., reposing comformably on the Avicula contorta series. 



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

 accustomed to regard the Lias formation as a great clay deposit, with a uniform fauna 

 throughout, still their accuracy may be clearly demonstrated in the extensive section on 

 the Dorsetshire coast, extending from near Bridport Harbour on the east to Pinhay Bay 

 on the west. Eor within these limits the entire series of beds rise beneath each other on 

 the shore, and are exposed in the clifi's, so that this coast section may be said to be com- 

 plete from the great arenaceous deposit of Upper Lias Sand, containing Harpoceras 

 opalinum, with each succeeding zone of the Upper, Middle, and Lower Lias, down to 

 Aegoceras 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 those of England by Sir 

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



This table likewise shows how completely the whole Lias formation is represented in 

 England, and how nearly it corresponds bed for bed with the Wiirtemberg series. I 

 shall now describe the different zones in ascending order, commencing with the zone of 

 Avicula contorta. 



As much difference of opinion formerly prevailed regarding the true position of the 

 Contorta zone, I have deemed it best to give a short account of the beds in question 

 for the purpose of showing how distinct their lithological and palseontological characters 

 are from those of the true Lias formation which rests upon them, and how necessary it is 

 to clear away all doubts as to the true affinities of these beds before entering upon the 

 study of the Lias formation which forms the subject of this introductory part of our 

 Monograph. 



