MESOZOIC ERA: THE AGE OF REPTILES 519 



by erosion to low, monotonous plains upon which few, if any, eleva- 

 tions of great height remained (p. 114). This being the case, the era 

 as a whole must have been one of great quiet, during which crustal 

 movements were uncommon. One should remember, however, that 

 at the close of the Triassic the faulting and elevation of the sandstones 

 and shales of that period occurred; that at the close of the Jurassic, 

 the Sierra Nevadas were raised, but that before the end of the Upper 

 Cretaceous even these elevations had for the most part disappeared. 

 The Appalachians were largely worn down to base level, and the 

 Laurentian region of Canada was a comparatively flat plain. Under 

 these conditions the streams of that time flowed in meandering 

 courses to the ocean, and the climate was probably uniform, warm, 

 and humid. 



Mountain-making Movements at the Close of the Mesozoic. — 

 During the closing stages of the Upper Cretaceous, great crustal 

 disturbances began which resulted in the formation of mountain 

 ranges from Alaska to the southern tip of South America. These 

 movements, following the long period of quiet just described, were 

 not sudden, but were anticipated by upwarping in Colorado, Wyo- 

 ming, and other places, as the presence of more abundant coarse sedi- 

 ments indicates. The great Rocky Mountains of Canada and the 

 United States had their birth at this time, but not their full growth 

 until later. The structure of these mountains is in marked con- 

 trast to that of the Appalachians, whose elevation was the result 

 of great lateral movements which folded and crowded together the 

 strata. Although horizontal compression was important in the for- 

 mation of the Rocky Mountains, the result of the vertical move- 

 ments is much more conspicuous (p. 364). The growth was also 

 assisted by faulting. In Utah the Wasatch and Uinta mountains 

 and in British Columbia the Gold Range were also raised. 



That the deformation did not take place previous to the Laramie 

 is proved by the fact that the strata of this stage and those of greater 

 age are folded with equal intensity, while the overlying Tertiary 

 rocks are less disturbed, showing that the deformation took place 

 before the deposition of the latter. In some areas, however, the 

 lowest Eocene (Fort Union and Wasatch) show as steep dips and 

 were apparently as much disturbed as the underlying Cretaceous, 

 indicating later deformation. These disturbances were accompanied 

 by volcanic eruptions and intrusions of lava. The laccoliths forming 

 the Henry Mountains of Utah were elevated by lava which was 



