the Earth* s Contraction from Cooling. 137 



The other is to the east of the Cretaceous axis in the summit 

 region of the Rocky-Mountain chain. A great thickness of 

 freshwater beds was made in the Green-River region and some 

 other places about the Rocky- Mountain summits, and thinner 

 deposits to the eastward. The thickness, in connexion with 

 evidences of shallow- water origin, indicates a progressing geo- 

 synclinal, although the ocean gained no entrance to it. The 

 downward bending ended probably just after the Miocene 

 period, without general displacements ; but there were tiltings 

 along the more western border of the Tertiary in the vicinity 

 of the Wahsatch and other mountains. (See note on page 135.) 



9. Since the Miocene era, and on through much of the 

 Quaternary, there have been vast fissure-eruptions over the 

 western Rocky-Mountain slopes. They had great extent, espe- 

 cially in the Snake-River region, where the successive outflows 

 made a stratum 700 to 1000 feet thick, over an area 300 miles 

 in breadth. There are other similar regions, but of less area. 



It is thus seen that along the Pacific side of the continent 

 the crust, under the action of lateral pressure, first bent down- 

 ward profoundly, and then yielded and suffered fracture and 

 plications, directly along a belt, parallel with the coast, either 

 side of the Great Basin (and perhaps over this basin to some 

 extent), the two great lines 400 miles apart. The plicated re- 

 gions thus made, having become firm by the continued pressure 

 and the engendered heat and resultant solidification, the crust 

 next bent, and then yielded, in a similar way, along an axis 

 outside of the former regions of disturbance, the two axes over 

 600 miles apart ; and again all was mended in the same way. 

 Then it bent a third time, just outside of the last range, on each 

 side of the same great area, the lines over 700 miles apart ; and 

 then over the western of the two ranges the beds were displaced, 



Big-Horn region between Long's Peak and Pike's Peak, near Denver in 

 Colorado, &c. Near the mouth of the Big Horn, the Chetish or Wolf 

 Mountains, consist of these upturned strata, and have a height of 1500 to 

 2000 feet above the Yellowstone. He found the later Tertiary beds some- 

 times tilted at a small angle, never over 10°. 



The discovery of Dinosaurian remains in some of the coal-beds, announced 

 by Marsh and Cope, and of Inocerami, as ascertained by Meek, is one part 

 of the evidence on which the lower parts of the coal-beds are determined to 

 be Cretaceous. Besides this, there is the fact that the supposed Miocene 

 of the Green- River basin contains remains of mammals that are decidedly 

 Eocene in character ; and if these are Eocene, then the coal-beds are some- 

 thing older. Professor Marsh is very strongly of the opinion that all the 

 coal-beds are Cretaceous. 



On the other side, Lesquereux states that the evidence from fossil plants 

 is totally opposed to making any of the coal-strata Cretaceous. 



The method of mountain-making, and the principle involved, are the same 

 whatever be the decision as to the exact epoch of the Cretaceous plication. 



Phil. Mag, S. 4. Vol. 46. No. 304. Aug. 1873, L 



