458 Sayles — Dilemma of Paleoclimatolo gists. 



versal warm climate without sunlight. For example, it is 

 difficult to explain the evolution of our flowering plants 

 and insects, and the feathers on birds and hair on mam- 

 mals, and the desert apparatus with which the camel is 

 furnished, without sunlight. Dr. Knowlton cites many 

 cases of annual rings of growth in fossil trees from Car- 

 boniferous to present time. Dr. Winifred Goldring 6 has 

 recently described Cordaites of Alleghany age from Okla- 

 homa which show pronounced growth rings, indicating 

 seasons in"35° N. latitude at that time. The seasons need 

 not necessarily have been cold and warm but may have 

 been wet and dry. How can such occurrences be 

 explained except by seasons! The Dead Sea is today 

 making seasonal deposits of mud with salt and gypsum 

 alternating regularly. In the past the same process went 

 on as- evidenced by the seasonal deposits of the Stassfurt 

 salts, of upper Permian age in Germany, and by the 

 Alsace salts, of Miocene age described by Gale 7 and 

 believed by him to be of seasonal origin. In Arizona 

 Shinier 8 described beds of gypsum and shale of Triassic 

 age, which alternate in a regular manner, and although he 

 did not say so, they are possibly of seasonal origin. 

 Blackwelder has recently made a study of oil shales from 

 the Green River region. This shale has very regularly 

 alternating brown and black bands. Blackwelder took 

 the specific gravity of the material of these brown and 

 black layers and found the former had an average speci- 

 fic gravity of about 1.9 and the latter about 1.3. This, in 

 the opinion of Blackwelder and the writer, is a case which 

 strongly suggests seasonal deposition. As time goes on 

 and the attention of geologists is called to such occur- 

 rences many more cases will doubtless be noted and 

 studied. Seasonal layers in glacial clays of Pleistocene 

 age have been known for many years, as described in the 

 works of DeGeer and a number of other geologists. 10 In 

 1915 the writer gave a paper before the Geological Soci- 

 ety of America describing seasonal banding in the slate 

 which occurs above the Squantum tillite in Boston harbor. 

 A paper comparing some Pleistocene clays in the Con- 

 necticut Valley with the Squantum Permo-Carboniferous 

 banded slates was published in 1919. As noted by 

 Coleman 3 and Barrell 11 and others, this comparison 

 leaves little doubt as to the same origin of the 



