MESOZOIC ERA: THE AGE OF REPTILES 571 



Alaska, in the Lower Cretaceous. If a cold, but not frigid, polar sea 

 existed from which currents extended southward, the apparent con- 

 tradiction in the evidence of the plants and animals would be ex- 

 plained. 



REFERENCES FOR CLIMATE 



Knowlton, F. H., — Succession and Range of Mesozoic and Tertiary Floras: Outlines 



of Geologic History (Willis and Salisbury), pp. 201-207. 

 Lull, R. S., — The Life of the Connecticut Trias: Am. Jour. Science, Vol. 33, 1912, 



PP- 397-422. 

 Schuchert, Chas., — Climates of Geologic Time: .Carnegie Institution of Washington, 



Pub. 192, 1914, pp. 263-298. 

 White and Knowlton, — Evidences of Paleobotany as to Geological Climate: Science, 



Vol. 31, 1910, p. 760. 



Coal 



Triassic. — Coal beds occur in the four systems of the Mesozoic. 

 In the United States, coal of the Triassic Age was worked as early as 

 1700 in the Virginia-North Carolina coal fields, but these deposits 

 are of more interest historically than economically. Coal of this 

 age occurs also in Germany, Sweden, South Africa, and Australia, 

 and, as in North America, is composed of horsetails, ferns, and 

 cycads. Coal in commercial quantities occurs in Hungary, in several 

 of the countries of Asia, in Australia, and New Zealand, in Jurassic 

 formations. 



Cretaceous. — The Lower Cretaceous rocks bear coal locally in 

 British Columbia and Alaska. The great coal-producing system of 

 western North America is the Upper Cretaceous, the total quantity 

 and extent of the coal formations being comparable to those of the 

 Carboniferous. The quality is, however, usually inferior to that of 

 the Carboniferous coal, being largely lignite, although some bitumi- 

 nous coal of excellent quality is produced, and in a few localities 

 anthracite coal, made from bituminous and lignite coal by the intru- 

 sion of igneous rocks, is worked. It is interesting in this connection 

 to note the presence of charred wood and charcoal in some of the Cre- 

 taceous beds, showing the existence of fire during the period. Al- 

 though workable coal is found in all the stages of the Upper Creta- 

 ceous of western North America, that of the Montana and Colorado 

 stages is most important. The so-called Laramie coal has been found 

 to belong largely to the Montana stage of the Upper Cretaceous and 

 to the lowest stage (Fort Union) of the Tertiary. 



