464 TWO TOARCIAN AMMONITES. [Nov. I903. 



of an ammonite- race ? The stages to which the Author had just 

 drawn attention always followed a regular sequence : a stage 

 might be omitted, or it might never be reached ; but those that 

 were observed were always in this sequence. If they could occur 

 anyhow, as suggested by the previous speaker, then, considering the 

 enormous number of ammonite-genera and species, the odds against 

 the sequence always being the same were very heavy indeed. 

 This was a matter of great importance, because if the principles of 

 ammonite-growth and evolution held by the Author and many others 

 were correct, then we were presented with an evolution that appeared 

 to follow regular laws of growth — neither fortuitous, nor governed 

 by contemporaneous cycles of external physical change. This did 

 not appear consistent with evolution by natural selection alone. 

 Further, this origination of new forms, whether species or muta- 

 tions, was of a very gradual nature, precisely similar to the growth 

 of an individual. This did not appear consistent with a theory of 

 evolution by discontinuous variation alone. Facts such as these 

 were, therefore, opposed to the DeVriesian no less than to the 

 Darwinian scheme. 



The Author, replying to the statements that the Geological- 

 Survey maps were only meant to be lithological charts, of use to 

 agriculturists, said he was afraid that even on these points they had 

 failed ; for those purposes the superficial deposits should have been 

 mapped first, instead of last. In solid geology, where Liassic clay 

 passed laterally into sands, it would have been easy to show both 

 contemporaneity and lithic change by the same colour dotted. Now, 

 the maps said that the sands were of later date than the clay, which 

 was incorrect. 



In quoting Ammonites sublcevis as having no spines, Prof. Blake 

 was most unfortunate. It had a spinous young stage, and was a 

 miniature Blagdeni. It was one of the best species to illustrate 

 those phenomena of cyclical development to which the Author had 

 drawn attention. 



