572 INDEX TO THE STEATIGRAPHY OF NOETH AMERICA. 



The latest account of the EUis formation in Montana is by Fisher/^^ who states 



that it — 



includes a basal limestone of variable thickness, ranging from 15 to 60 feet, which in places 

 merges upward into a coarse conglomerate that passes into a medium-grained sandstone, light 

 brown to gray in color and more or less thin bedded. In other localities, however, the change 

 from limestone to conglomerate is abrupt. The limestone and conglomerate contain marine 

 Jurassic invertebrate fossils. Some of those in the conglomerate are fragmentary, but more 

 are complete, with pebbles of limestone and quartzite several inches in diameter. The com- 

 ponent parts of the conglomerate are bound together by a calcareous cement. The total thick- 

 ness of the formation is about 80 to 120 feet. It rests unconformably upon the shale of the 

 Quadrant formation in certain parts of the field, and upon the Madison limestone in others. * * * 

 The following sections illustrate the succession of the beds of the formation in different 

 parts of the field: 



Section of Ellis formation near Goodman siding, Montana,. 



Feet. 

 Sandstone, massive, light brown to gray, weathering tan, conglomeratic and fossiliferous at base. 66 



Limestone, reddish brown, fossiliferous 6 



Beds concealed (estimated) 18 



90 

 Section of EUis formation at head of Ming Coulee, Montana. 



Feet. 



Sandstone, gray, weathering brown, thin bedded 60 



Sandstone, gi'ay, conglomeratic, containing marine Jurassic fossils 29 



Limestone, dove-colored, massive; basal member brecciated and containing Jurassic fossils. . . 60 



149 

 Fossil invertebrates, mainly Ostrea and Camptonectes, are present in great abundance in 

 the two lower members of the above section. The numerous specimens of these genera and a 

 few other forms are suificient to determine that the rocks belong to the Elhs formation, which 

 in the Yellowstone National Park and neighboring areas 3delds a characteristic upper Jurassic 

 fauna. The sandstone of the Ellis formation throughout the Great Falls region is usually not 

 fossihferous, but the conglomerate and underlying limestone contain an abundance of Jurassic 

 fossils. 



The Morrison formation, which :s regarded as probably Jurassic by some 

 geologists, is described with the Lower Cretaceous in Chapter XIV (pp. 606-608). 



L-M 10. OLYMPIC PENINSULA. 



Arnold ^^ refers to supposed pre-Cretaceous rocks in the Olympic Peninsula of 

 Washington, which he mapped as Jurassic and which are so shown on the map of 

 North America, as follows: 



The formations involved in the geology of the coastal region of the Olympic Peninsula 

 include serpentine, old diabase or greenstone, metamorphosed sandstone and quartzite, prob- 

 ably of Jurassic age; 6,000 feet of gray sandstone with minor quantities of carbonaceous shales, 

 supposed to represent the lower part of the Puget group and of Cretaceous age; 1,200 feet of 

 basalt and basalt tuffs of Eocene age; 15,000 feet of Oligocene-Miocene conglomerate, sand- 

 stone, and shale; 2,260 feet of Pliocene conglomerate, sandstone, and shale; and at least 300 

 feet of Pleistocene till, clay, and gravel. In addition to this, the Oligocene-Miocene breccia 

 contains large quantities of angular fragments of hard black slate, indicating a probable wide- 

 spread formation of this type of rock somewhere in the general region. Nothing is known of 

 the age of the slate except that it is pre-Oligocene. 



The supposed pre-Cretaceous rocks of the territory examined were confined entirely to the 

 coast south of Cape Flattery, the most important areas occurring at Portage Head, 8 miles 



