CRISES IN EVOLUTION 2il 



Triassic " New Red Sandstone," and the proofs of 

 enormous denudation prior to the commencement of 

 Tertiary sedimentation, must be accepted as represent- 

 ing long intervals of time, during which organic evolu- 

 tion will have made great progress, even if proceeding 

 at its normal rate. 



When the records of these critical times are studied in 

 distant regions, the boundaries between eras often prove 

 no less obscure than those between their several periods, 

 both in Stratigraphy and Palaeontology. The familiar 

 term " Fermo-Trias " expresses the uncertainty surround- 

 ing separation of the Palaeozoic and Mesozoic, while the 

 difficulty of determination of the upper limits of the 

 Carboniferous and diversity of opinion as to the value 

 of the Rhaetic show that the division between the two 

 eras cannot be shifted in either direction with better 

 hopes of precision. The Ammonites, which appear so 

 suddenly in our Liassic record, were the descendants of 

 forms that flourished elsewhere in Permian as well as in 

 Triassic times. The first Belemnite certainly seems to 

 have been Triassic, but so was the last Orthoceras. 



In many parts of Europe there is comparable reason 

 for hesitation in drawing a line between the Cretaceous 

 and Eocene. The faunas of the Maestrichtian and 

 Danian stages (unrepresented in Britain) show steadily 

 increasing " Tertiary " qualities as they are traced 

 upwards. Most Cainozoic Invertebrate groups range 

 back to the Cretaceous, if not farther ; while Belemnites, 

 at least, lingered after Mesozoic times. Teleodonts and 

 Ctenobranchs had climbed far towards their acmes before 

 Ammonoids disappeared. 



In fine, the world-evidence at present available seems 

 to point towards a negative answer to the two first 

 questions asked in the opening paragraph of this 

 chapter. It is perhaps perilously hypothetical, but at 



