212 HISTORICAL GEOLOGY 



Economic Products 



Coal beds of some commercial value occur in the Triassic rocks 

 of Virginia and North Carolina. 



Enormous quantities of sandstone (the so-called "Triassic 

 Brownstone") for building purposes have been quarried from the 

 Newark series, especially in the Connecticut River Valley. 



Gypsum of Triassic age is quarried in some of the western 

 states. 



Some copper deposits occur in Triassic rocks of California and 

 Alaska. 



Life of the Triassic 



The physical revolution which closed the Paleozoic era was 

 accompanied by one of the most profound changes in organisms 

 in the earth's histoiy, and hence we may expect the life of the 

 Triassic to have been very notably different from that of preceding 

 time. Some types of animals and various types of plants continued 

 from the late Paleozoic, but the general aspect of Triassic life was 

 distinctly more modern than that of the Paleozoic. In spite of 

 this comparatively rapid evolutionary change in both fauna and 

 flora, enough connecting links are known to make sure that the 

 Mesozoic animals and plants were derived from the Paleozoic. 



Plants. — Triassic plants have not left us a very abundant 

 record. In fact the rather widespread aridity of climate doubt- 

 less hindered a luxuriant growth, over wide areas at least. 



Among the simple plants (Thallophytes) the calcareous Sea- 

 weeds, that is those which had the power to secrete limey skeletons, 

 were especially common. 



Among Pteridophytes the Ferns and their allies were still im- 

 portant; the Equisetce were fairly common, though much more like 

 the existing forms except for their greater size; and the Lycopods 

 were reduced almost to extinction, even the few lingering Sigil- 

 larians having finally disappeared with this period, so that the 

 Lycopods will not again call for special mention. 



Gymnosperms were the dominant types of plants of the Tri- 

 assic, just as Pteridophytes had been the dominant plants of the 

 later Paleozoic. The Cordaites were greatly reduced and they be- 

 came extinct during this period. Cycads and their allies and the 

 Conifers (Fig. 126), however, were the most common elements of 



