MIDDLE LIAS. 



67 



THE MIDDLE LIAS. 



The Middle Lias is well developed in England, and fully exposed in the grand 

 natural sections of the Yorkshire and Dorsetshire coasts. In the Midland Counties some 

 of the zones are only partially shown. I have therefore selected a section of the cliffs east 

 of Charmouth, Dorset, which I made for this work many years ago, as one that affords 

 a good general view of the whole, and at the same time shows the relation of its 

 spinatus-hed to the Upper Lias which rests conformably upon it ; the Middle Lias here 

 attains a thickness of about 450 feet, and is divisible into five stages, each characterised 

 by well-determined Ammonite forms. In ascending order these are — 1st. The zone of 

 Aegoceras Jamesoni. 2nd. The zone of Amaltheus Ibex. 3rd. The zone of Aegoceras 

 Henleyi. 4th. The zone of Amaltheus margariiatus. 5th. The zone of Amaltheus 

 spinatus. 



Section of Down Cliffs, at ToacPs Com, near Bridport Harbour. 



Upper Lias. 



Alti- 

 tude. 



No. 



LlTHOLOGY. 



Thick- 

 ness. 



Organic Remains. 



ft. 

 400 



300 



1 

 2 



3 



4 



Zone of Haupoceras opalinum. 



Zone of Lytocebas Jurense. 



Brown sands, sometimes micaceous, 

 with large sandstone nodules iu 

 layers 



ft. 



70 



72 



2i 



Harpoceras opalinum, Rein., at Burton Cliif, 

 and Chideock Hill. 



Harpoceras variabile, d'Orb. 

 Harpoceras insigne, Schliib. 



Harpoceras bifrons, Brug., Pleuromya uni- 



oides, lloem. 

 Fossils rare, and often indeterminable. 



Harpoceras serpentinum, Schlot., Stephano- 

 ceras commune, Sow., S. Raquiuianum, 

 d'Orb., Venus pumila, Miinst., Rhynch. 

 acuta, Sow., and Rhynch. Moorei, Dav. 



Zone of Harpoceras bifrons. 



Dark-greyish sandy marl, very mica- 

 ceous 



Zone of Harpoceras seepentinum. 



Brownish marly limestone, containing 

 great numbers of Harpoceras ser- 

 pentinum and Upper Lias shells. 

 The Middle Lias comes up to the 

 /ower part of this band of stone, with 

 Amaltheus spinatus embedded there- 

 in 





