156 GEOLOGICAL SUEVEY OF THE TERRITORIES. 



than in tbe remaining portions of the park. These may represent small 

 portions of the Jurassic caught between the Cretaceous and the under- 

 lying archsean ; and if so, the Jurassic should be represented as occur- 

 ring in the park. On the other hand, however, they do not strongly 

 resemble the variegated arenaceous shales of the Upper Jurassic, which, 

 both east of the range and west of the park, occur below the Lower 

 Cretaceous, while they do contain thick beds of siliceous sandstone 

 very like those characterizing the undoubted No. 1, just above; and, 

 moreover, in beds laid down upon a newly-prepared sea-floor of far older 

 and non-conformable rocks, as these were, unevennesses of the under- 

 lying surface and corresponding abrupt changes of thickness of the 

 newer beds are to be expected. I have, therefore, in view of these con- 

 siderations, and in the absence of fossils, regarded these beds as form- 

 ing a portion of the Cretaceous No. 1. The transition between No. 1 

 and the slates above is abrupt, while the shales of No. 4 and sandstones 

 characterizing No. 5 appear to commingle, giving no marked line of sep- 

 aration between them. As was first distinctly pointed out by New- 

 berry* east of the range, so here in the middle park, the general aspect 

 of the formation as a whole is that of a " circle of deposition," an en- 

 croaching shore-line deposit of sandstones attending slow submergence, 

 followed by a deeper water sediment forining slates and shales, but not 

 reaching sufficient depth or attaining the proper conditions to develop 

 extended limestone deposits ; in turn followed by a shallowing sea, with 

 more arenaceous accumulations. The latter shallowing x>robably accom- 

 panied, perhaps as an effect of the same cause, the formation of a gen- 

 tle anticlinal fold, found along the lower portion of the Grand Eiver, 

 and which occurred shortly after the deposition of the No. 5 sandstones, 

 and before the laying down of the next great sedimentary deposit, as 

 will be seen later. 



A thin seam of coal occurs in the lower mid-cretaceous slates, a few 

 hundred feet above the quartzitic sandstones of No. 1, at the Hot 

 Springs, indicating that coal-forming conditions existed far below the 

 usual lignite horizon just east of the range. The latter, as shown later, 

 seems to be also found in the i^ark, but very poorly indicated. 



DOLERITIO BRECCIA. 



Above the Cretaceous No. 5 the next youngest rock is a local occur- 

 rence of volcanic doleritic material, consisting partially of subaqueous- 

 arranged material — dolerite, tuff, and breccia — and partially as accom- 

 panying lava-flows ; in all, reaching a maximum thickness of 800 or 900 

 feet. 



THE LIGNITIC FORMATION OF THE PARK. 



Eesting ' upon the latter when it occurs, but elsewhere upon Creta- 

 ceous No. 5, and apparently conformable with the latter, except at one 

 point where there is a decided unconformability, is a series of beds 

 which reach a thickness of about 5,500 feet. Not being capped with 

 any beds following them in direct geological sequence, it is impossible 

 to tell how much thicker they may originally have been, erosion having 

 already removed an unknown amount of them. They are composed in 

 part of sandy shales, in places more or less argillaceous and quite soft, 

 spaced rather regularly with more prominent and characteristic hori- 



*Americaii Assoc, meeting, Newport, R. I., 1860 ; also, later, Proc. Am. Assoc, Aug., 

 1873, p. 185, «fcc. 



