Diener — Critical Phase in History of Ammonites. 125 



been advocated very strongly by C. Schuchert, 3 who 

 insists on a general lowering of the temperature during 

 the Liassic period, chiefly on the strength of the argu- 

 ments of Handlirsch. I am happy to agree with this 

 learned author in the opinion that the facts which prove 

 the influence of climatic changes are many and weighty, 

 but I think that the extinction of Triassic ammonites at 

 the close of the Rhaetic does not admit of this explanation. 



It can hardly be too often repeated that the decay of 

 ammonites, near the close of both the Triassic and Creta- 

 ceous periods, was gradual, that in the first instance it 

 clearly began in the Upper Noric and continued through- 

 out the Rhaetic. Now, we are well informed about the 

 climatic conditions of Upper Noric time, due to the dis- 

 covery of rich faunae of reef -building corals in this sub- 

 stage. Such faunas are known to us from the Austrian 

 Alps, from Timor, Nevada, Oregon and Alaska. J. Per- 

 rin Smith demonstrated the identity of nearly all his 

 Alaskan species with types from the Upper Noric Zlam- 

 bach beds of the Salzkammergut. The presence of this 

 fauna under the 60th degree of north latitude is contra- 

 dictory to the suggestion of a lowering of temperature in 

 the Upper Noric seas. It may be equally well to call 

 attention to the wide distribution of several species of 

 ammonites and bivalves (Pseudomonotis ochotica) 

 throughout the Pacific Ocean and into the arctic region 

 (New Siberia), which is in favor of a comparatively 

 equable but not of a low temperature. 



Nor does the flora of the Rhaetic stage exhibit any traces 

 of increasing cold. It is of a remarkable uniformity in 

 North America, England, Sweden, Germany, eastern 

 Greenland, Spitzbergen, Persia, India, Japan, China, New 

 South Wales, New Zealand, South Africa, Argentina, 

 Chile and Honduras, and seems to prove a climate more 

 uniform and milder in the polar regions than that of the 

 present day. 



If a period of cooling set in at the close of the Rhaetic 

 epoch — and I do not dissent from Professor Schuchert 's 

 opinion in this respect — it came too late to influence the 

 extermination of Triassic ammonites, for this had been 

 heralded long before by their gradual decay. 



3 Ch. Schuchert, Climates of geologic time, Carnegie Inst. Washington, 

 Publ. Xo. 192, p. 284. 



