EVOLUTION OF THE EARTH'S FEATURES. MOUNTAIN-MAKING. 751 



black hydrocarbon shales (like the Black shale of the Hamilton), to 

 be condensed in cavities in overlying strata. The heat engendered, 

 and causing the metamorphisni, may be so great as to reduce the rock 

 subjected to it to a plastic condition, and make granite, or some 

 other granite-like rock ; in which case, granite may be made to fill 

 opened fissures, like a true igneous rock, or to constitute the core of 

 a long mountain range, like that of the Sierra Nevada. 



9. The region of a Synclinorium becomes added to the stable part 

 of the Continent. — The region that had been long undergoing sub- 

 sidence becomes, after the upturning and consolidation, stiff, unyield- 

 ing, and stable ; and the locus of the next progressing geosynclinal 

 on the same continental border will be situated to one or the other 

 side of it. After the Alleghany range was made, there was, in the 

 next, or Triassic period, a new trough, or rather a series of them, more 

 to the eastward, in which the Triassico-Jurassic beds were laid down. 



On the Pacific Border, there were geosynclinals in progress, from 

 the early Paleozoic onward, in the regions of the Sierra Nevada, the 

 Humboldt Mountains over the Great Basin, and the Wahsatch just 

 east of the Great Salt Lake ; aud, after the Jurassic period, the catas- 

 trophes occurred in which these great mountain ranges, or synclinoria, 

 were made. Next, there were two geosynclinals in progress during 

 the Cretaceous period, outside of these, one east of the Wahsatch, and 

 the other in California, west of the Sierra Nevada ; and, in the early 

 Tertiary, both of these ended in synclinoria. Next, these regions 

 having thus become part of the stable land, two other geosynclinals, 

 some thousands of feet in depth, were in progress, one farther west in 

 California, and the other farther east in Wyoming, Colorado, etc. 

 They continued sinking until the close of the Miocene Tertiary, when 

 that on the west ended in mountain -making, 'adding ridges, 2,000 to 

 3,000 feet in height, to the Coast range ; and that on the east experi- 

 enced some small displacements. There were hence two parallel 

 series, cotemporaneous in steps of progress, on opposite borders of 

 the Great Basin, a coast-series, and a mountain-series, each having its 

 highest member toward the basin ; the coast-series the grandest in its 

 three parts, and leaving evidences of the profoundest disturbance, and 

 the greatest amount of metamorphism. The Wahsatch range is nearly 

 as high as the Sierra ; but probably a fourth of its height is due to 

 the final elevation of the Rocky Mountain region. 



10. Geanticlinals as well as Geosynclinals concerned in Mountain- 

 making. — In the movements of the earth's crust, there would neces- 

 sarily be upward as well as downward flexures — that is, geanticlinals 

 as well as geosynclinals. The Appalachians, as explained above, may, 

 when first made, have stood up in lofty ridges, without having under- 



