92 Smith — The Occurrence of Coral Reefs 



Art. XI. — The - Occurrence of Coral Reefs in the Triassic 

 of North America ;* by James Perrin Smith. 



The occurrence, in the strata of past ages, of reef-building 

 corals of modern groups gives us our best record of climatic 

 conditions in those times. The modern reef-builders are now 

 confined to the tropics, and it is only reasonable to assume that 

 they have always been confined to regions where the waters 

 had a tropical temperature. 



No corals of any sort are known as yet in the Lower Triassic, 

 anywhere in the world, although the Hexacoralla must have 

 lived somewhere during that time, since they are known before 

 and after it. In the Middle Triassic of the Alpine province 

 reef -building corals occur, but are not abundant enough to 

 form reefs. They are not vet described from any other region. 

 Towards the end of the Upper Triassic reef-building corals 

 became abundant in the Alps, where they have long been 

 known, and where they formed genuine reefs that had an 

 important influence on the topography. There they extend up 

 to latitude 45° N., showing that in this epoch the Alpine 

 province enjoyed a warm climate. The chief coral zone of 

 the Alpine province occurs in the Noric epoch of the Upper 

 Triassic, not far above the rich ammonite limestone of the 

 Karnic epoch. The occurrence of this same coral fauna, in the 

 same stratigraphic position, in localities far removed from the 

 Mediterranean Region would be ample proof that the favor- 

 able conditions were widely distributed over the earth in this 

 epoch. This would also tend to show the probability of the 

 amelioration of the general temperature, at least over the 

 northern hemisphere, during this epoch. 



Reef-building corals have been found in the Himalayas in 

 India in the Noric beds, but are not yet described ; their evi- 

 dence as to physical conditions is just as positive, even though 

 we do not yet know by what names they should be called. 



In his studies of Triassic stratigraphy in northern California 

 the writer was long ago impressed by the fact that the lime- 

 stone there resembles coral rock, and fragments were found 

 that suggested remains of corals. Several years ago this was 

 confirmed by the discovery of abundant corals in many places 

 on the limestone ridge between Squaw Creek and Pitt River, 

 and on Cow Creek south of Pitt River. The general section 

 of the Triassic of Shasta County is given below, to show the 

 position of the coral zone. 



In the section given above, the thickness of the beds is only 

 approximate, varying from the maximum near the junction of 

 * Published with permission of the Director of the U.S. Geological Survey. 



