106 PEOF. J. LOGAN LOBLEY, F.G.S., F.R.G.S., ON 



litliologically to the Permian than to the Jurassic rocks, but the 

 Triassic fauna is much more Hke the Jurassic fauna above than 

 that of tlie Permian below. 



The EhcTtic limestones and shales of England are very 

 similar to the Lower Lias limestones and shales, indicating 

 similar marine conditions. Yet our EliDetic beds are without 

 ammonites and belemnites, without many genera of Brachipoda, 

 Lamellibranchiata and Gasteropoda, and without Ichthyosaurus 

 and Flesiosaurics, all of which genera are most conspicuous in 

 our Lower Lias. The Bathonian and the Portlandian marine 

 conditions, both giving thick-bedded oolitic limestones, must 

 have been very similar, but while Brachiopoda are most 

 abundant in the Bath limestones, they are entirely wanting in 

 the Portland limestones, and although ammonites are present, 

 belemnites are absent. 



On the other hand, very considerable alterations of environ- 

 ment have been accompanied by very small biological change. 

 Trilobites are in the shales as well as in the limestones of the 

 Silurian rocks, although these greatly differing deposits indicate 

 at one time abundant argillaceous matter in shallow seawater 

 and at another a clear and deeper sea. 



So also do ammonites and belemnites abound both in the 

 Jurassic limestones and the Jurassic clays, while in Cretaceous 

 rocks they are both in the calcareous Chalk and the 

 argillaceous Gault. The range in time of the Orders and 

 genera of Cephalopoda, indeed, present several remarkable 

 features. Tetrabranch cephalopods have lived through all 

 conditions from Lower Silurian times to the present, while 

 •dibranchiate cephalopods appear in Secondary times. Two 

 conspicuous tetrabranchs, the Naidilus and the Amvionite, with 

 the dibranchiate Belemnite, Romished throughout the Secondary 

 period under the same marine conditions, but at its close the 

 tetrabranch Ammonite and the dibranchiate Belcmnite became 

 extinct together, while the Nautilus which lived in Palaeozoic 

 seas continued to live and is still abundant. Again the 

 tetrabranchiate Orthoceras died out in Triassic times while then 

 it was that the Amnionoidea of the same Order had its greatest 

 development, ] ,000 species having been described. 



And so it appears to have been with terrestrial organisms 

 also, if we may judge from the comparatively few land fossils 

 that have been preserved. Nothing could well be more 

 different in land surface conditions than the warm and humid 

 and low-lying conditions of the Coal Measure areas, and the 

 cool and breezy and elevated conditions of our mountain sides. 



