SECTIONAL TRANSACTIONS.— C. 317 



and passing up into the St. Bees Sandstone are ' liaison ' deposits between the 

 Permian and the Trias, but it is still difficult to accept this horizon as the boundary 

 between the Palseozoic and Mesozoic eras, as it is bridged by the deposition of breccias 

 formed under similar climatic conditions throughout Permian and early Triassic times. 



It would be, indeed, a great convenience to British geologists if we could consider 

 the rocks deposited after the zenith of the Hercynian movements in this countrj'' as 

 belonging to the Mesozoic, and if we could combine the Permian and Trias into one 

 system ; but in this we might be ignoring the significance of the great unconformity 

 due to the movements. Our Permian rocks may be but poor representatives of the 

 Upper and a little of the Middle Permian. 



In dealing with continental and non-fossiliferous deposits, one is apt to fall easily 

 into traps. Dr. Sherlock thinks that the St. Bees Shales represent the ffiddle Permian 

 Marl. This cannot be proved ; but since we now consider the Magnesian Limestone 

 of Whitehaven to be the Middle Limestone — the St. Bees Shales may represent the 

 Upper Limestone — the Upper Permian Marls and part or the whole of the Lower 

 Mottled Sandstone — who can tell ? 



To my mind the evidence for establishing the validity or otherwise of the system 

 does not occur in this country. To attempt to tackle the problem at this end appears 

 to me to be like grasping the wrong end of the stick. 



Prof. D. M. S. Watson, F.R.S. — It is the commonly accepted belief of geologists 

 that Systems should be defined as the periods of time between great diastrophic 

 events, which will produce either marked unconformities or great changes of fauna, 

 effects visible over a large part of the world. Thus the rocks which belong to a definite 

 system should not be connected by passage beds to those of tlie nest and should in 

 general be unconformable to those below. 



Application of these criteria to Britain would lead to the abolition of the Devonian 

 System, the Lower]01d Red Sandstone being added to the Silurian and the upper to the 

 Carboniferous, of the Permian System whose lower half would form the top of the 

 Carboniferous, whilst the rest would form a beginning of the Trias, and of the Jurassic 

 which passes down conformablj' and through passage beds into the Trias. Thus 

 British geologists have not in fact delimited Systems by the criteria which are 

 assumed to be used. 



The validity of a system depends on its usefulness ; and this on the length of 

 time it represents as judged from thickness of strata and from the extent of evolutionary 

 change which takes place within it. 



The Amphibia and bony fish of the Lower Carboniferous of Scotland do not differ 

 recognisably in their evolutionary grade from those of the Middle Coal Measures of 

 Europe and N. America, which represent the same facies. 



The Amphibia from the Stephanion of Nyram are clearly somewhat more 

 advanced than those of Linton, Ohio, and other Middle Coal Measure faunas. 



The Lower and Middle Rothliegende Amphibian faunas of Europe clearly represent 

 in part a further development of those of the Coal Measures and of Nyram, but they 

 include a few rare forms which agree with the far larger dry land fauna of the 

 Artinskian of Texas, whose age is fixed by interbedded ammonites. 



The Tetrapod fauna of the Copper-bearing Sandstones of the Urals, which are 

 supposed to be about of the age of the Kupferschiefer, contains some animals 

 (Zygosaurus) which tie it to the Texan fauna and others which are morphologically 

 intermediate between the Texan Pelycosaurs and the S. African Tapinocephalus zone 

 Deinocephalia. 



The Karroo System exhibits the steady evolution of a fauna from the Tapino- 

 cephalus zone M. Permian, through the Cisticephalus zone whose fauna agrees with 

 the Zechstein fauna of the North Dwina to the L. Triassic Cynognathus zone. 



This series is then interrupted by the Coal Measures of the Molteno series which 

 yield no identifiable reptiles, and the fauna of the overlying Red Beds, though 

 theoretically capable of derivation from that of the lower zone, is far more advanced 

 and agrees with those of the Upper Trias of the Northern Hemisphere. 



The evolutionary change which is shown by a comparison of the Reptiles and 

 Amphibia of the U. Permian Cisticephalus zone with those of the L. Permian of Texas 

 is very great indeed, vastly more important than that which distinguishes the 

 Stephanian from a Lower Carboniferous fauna and at least as great as that which 

 occurs during the Trias. 



