the Earth's Contraction from Cooling. 135 



tions are included. The granite axis of the chain probably 

 indicates, as LeConte has suggested, the region of maximum 

 disturbance and metamorphism. 



The "Wahsatch contains, according to Clarence King, forma- 

 tions of all the ages from the Lower Silurian to the Jurassic ; 

 and the whole are throughout conformable; and a great thick- 

 ness of crystalline rocks exists beneath, supposed to be Archaean, 

 which he states are conformable also. The plications and 

 mountain-making took place, as King states, contemporaneously 

 with the same in the case of the Sierra, before the Cretaceous 

 era, the Cretaceous beds lying on the Jurassic unconformably. 



These two synclinoria are 400 miles apart. The preparatory 

 geosynclinal of the Wahsatch, and probably that of the Sierra, 

 took for its completion, supposing it to have begun with the 

 opening Silurian, a period at least a fifth longer than the whole 

 Palseozoic. 



5. At the close of the Cretaceous another pair of geosyn- 

 clinals, parallel with the coast, but geosynclinals of only Cre- 

 taceous origin, culminated in synclinoria. 



One of the Cretaceous geosynclinals was in progress east of 

 the Wahsatch, along the whole summit-region of the Rocky 

 Mountains in the United. States. Directly east of the Wah- 

 satch, according to King, the beds are 9000 feet thick, or more; 

 and, as Hayden states, they have a great thickness in the La- 

 ramie Plains, and little less over the upper Missouri region, so 

 that the downward movement was in some parts a profound one, 

 and affected a very wide extent of country. Hayden and King 

 make this disturbance to have taken place after part, or all, of 

 the Eocene period had passed, while Prof. Marsh holds that it 

 occurred at the close of the Cretaceous period*. 



* Clarence King has very briefly described the Wahsatch region, as well 

 as the country to the west, in the third volume (4to, 18/0) of his United- 

 States Geological Exploration of the 40th parallel j and on page 454 he 

 says : — " Subsequent to the laying down of the old cretaceous system, and 

 of those conformable freshwater beds which close the coal-bearing period, 

 another era of mountain-uplifts occurred, folding the coal series [Creta- 

 ceous and Lower Tertiary] into broad undulating ridges having a general 

 trend north-east." He then observes that freshwater Tertiary beds of 

 sand and clay, " an immense accumulation/' were laid down unconform- 

 ably over this upturned Cretaceous, and, after the Miocene era, were sub- 

 jected to " orographic " disturbances and "tilted to an angle of 15° to 20°, 

 or thrown into broad and gentle undulations wherever they lie in the 

 neighbourhood of the older ranges, such as the Wahsatch and Uintah/' 

 These disturbances were confined to within fifteen miles of the Wahsatch. 

 The period in which they occurred witnessed also great outflows of trachytic 

 rocks in this and other parts of the Rocky-Mountain region. Mr. King 

 adds, on page 455, that there is no question as to the identity of the beds 

 that overlie unconformably the Cretaceous folds along the eastern flank of 

 the Wahsatch with the horizontal Tertiary deposits of the Green-River 



