88 
THE GEAND GASTON DISTRICT. 
trasted in the terraces — the Jura being one vast indivisible mass of white 
sandstone — the Trias being composed of very many thin and often shaly 
beds of most intense color — yet in proceeding southeastward the Trias loses 
many of its layers, and those which remain are thicker and more massive; 
while the Jura gradually becomes red and shows here and there well-marked 
planes of subdivision. In a word, the two formations become more and more 
alike as we trace them south eastwardly. Between the Grlen Canon and the 
Triassic exposiu’es of New Mexico is an interval of 80 to 120 miles in which 
no explorations of a critical character have been made, and we are therefoi’e 
ignorant of the nature of the transition by which in this unexplored interval 
the identity of the Jurassic sandstone is lost. So far as present knowledge 
is concerned we are at liberty to suppose (1), either that the Jurassic sand- 
stone thins out completely in the interval, or, (2), that it becomes the sum- 
mit of the presumed Trias of New Mexico and cannot be distinguished from it. 
The sandstones of both formations are alike destitute of distinguishable fossils. 
Like the Eocene and the Cretaceous, the Jurassic has its littoral belt 
skirting’ the shore of the old Mesozoic mainland of the Great Basin. All 
the way from the Wasatch southward through central and southwestern 
Utah, thence obliquely into Nevada, without known limits, are found the 
detached exposures of this formation, faulted and displaced after the man- 
ner peculiar to the region. Around the southern flanks of the Markdgunt 
and Paunsdgunt the exposures of the Jurassic are very grand aaid impressive. 
Here it is no longer displaced from sensibly horizontal positions but shows 
many buttes and outliers. None of them are far distant from the principal 
mass. Further eastward the formation is disclosed in an equally conspicu- 
ous manner in the Paria amphitheater. Upon the eastern side of this amphi- 
theater it forms the base courses of the Kaiparowits, and descending east- 
ward by a monoclinal flexure it disappears beneath the immense masses of 
Cretaceous strata which constitute the body of that plateau. All along the 
western wall of the Kaiparowits, as far as the Colorado, it holds this rela- 
tion, exposing its edge upon the upturn of a monocline at the foot of the 
plateau wall. Beyond the Coloi’ado the same relation continues in the 
Echo Clitfs, along the base of which runs the same flexure; and high above 
the Trias, but beneath the Cretaceous, the Jurassic appears duly in its 
