830 HISTORICAL GEOLOGY. 



The Fort Union group (first examined by Hayden in 1860) also was placed in this 

 connection by Meek, on the ground of its fresh-water shells and lignite. The group was 

 estimated by Hayden to have a thickness of 2000'. He reported it (1871) as extending 

 southward from Fort Union, across the Yellowstone between the Black Hills and Eig Horn 

 Mountains, and northward into British America ; but the conclusions were not based on 

 a full study of the region. The 150 feet of deposits exposed near Fort Union include three 

 beds of impure "lignite," 1', 1-5', and 4 inches thick, alternating with beds of indurated 

 clay and clayey sands, 20' to 70' thick containing occasionally land shells and some leaves. 

 The age of the Fort Union beds has remained doubtful. Newberry (1890) separated it 

 from the Laramie on the ground of differences in the plants ; L. F. Ward refers it on the 

 same ground to the Upper Laramie. 



The beds in Middle Park, Col., referred to the Denver horizon by Cross, consist 

 largely of andesytic breccia, sand-beds and conglomerates, and are 800'-900' in thickness 

 (Marvine). They rest on upturned Cretaceous strata. 



Underneath the Fort Pierre group in the Belly Biver district, Canada, fresh-water 

 beds occur containing fossil leaves, which have been called the Bellij Biver group. The 

 plants are in part identical with the Laramie (Dawson, 1886). The Dunvegan beds, on 

 Peace River, are supposed to be of the same age. A large area has been referred to the 

 Laramie in British America extending from the United States boundary to the 55th paral- 

 lel, and eastward to 111° W. ; in it have been recognized a Lower Laramie or St. Mary 

 River series ; a Middle, the Willow Creek beds ; an Upper, or Porcupine Hills beds, which 

 correspond in fossils to the Souris River beds, just north of the United States boundary. 

 A more eastern area extends from 49° N. to 51° N., between 102° and 109° W. 



In Manitoba, Central North America, the Cretaceous formation is nearly 2000' thick ; 

 and the Montana group contains in its lower part many Rhizopod shells with some Radio- 

 larians. The thickness of the Dakota beds in this region is 13' to 200' ; of the Colorado 

 beds, 200' to 700' ; and of the Montana, over 1000'. The Cretaceous rests unconformably 

 on the Devonian (J. B. Tyrrell, 1892). Fossil plants from Laramie beds in the Mackenzie 

 River have been described by Dawson (1882 to 1889) and identified with others from 

 Alaska. 



Pacific Border. 



On the Pacific Border, the Upper Cretaceous, or the Chico beds, occupies 

 a broad belt extending originally from Lower California northward beyond 

 the Queen Charlotte Islands. It formerly covered the region of the Coast 

 and Cascade ranges, reaching the western base of the Sierra Nevada in Cali- 

 fornia, and of the Blue Mountains in Oregon. Its eastern limit is indicated 

 upon the map on page 813. 



The Upper Cretaceous of California includes only the Chico beds of the Shasta-Chico 

 series. The Tejon, which Gabb considered Cretaceous, has been shown by Conrad, 

 Heilprin, and White to be Eocene. The Wallala beds of White and Becker (1885), 

 according to Dall and Fairbanks (1893), are only a phase of the Chico. The Chico beds 

 are exposed upon both sides of the Sacramento valley. Thence they extend southward 

 near the coast to Lower California, according to Lindgren and Fairbanks, and northward, 

 with local interruptions, to Jacksonville, and Riddles, Oregon ; and beneath the covering 

 of later lavas they are supposed to connect with the Chico of eastern Oregon (Diller). The 

 lower portion of the Chico beds consists chiefly of sandstone and conglomerate, and ranges 

 from 900' to 1400' in thickness. In the upper portion shale predominates, excepting near 

 the shore line where the sediments are generally coarse. The greatest thickness of the Chico, 

 according to Diller, is nearly 4000' in Tehama County, Cal.; it thins out northward and 



