542 n. h. dart0n fish remains in ordoviclan rocks 



Introduction 



The purpose of this paper is to announce the discovery of fish remains 

 in rocks of Ordovician age in the Bighorn mountains and to describe the 

 character and relations of the rocks in which they occur. There will be 

 added a few statements regarding the similar occurrence of fossil fish in 

 the Ordovician sandstone near Canyon City, Colorado, announced by Mr 

 C. D. Walcott in 1892f, and a brief review of our knowledge of the 

 Ordovician geology of the Northwest. 



General Geology of the Bighorn Uplift 

 geography 



The Bighorn mountains are an outlying portion of the Rocky Mountain 

 range, extending from north-central Wyoming into the south-central por- 

 tion of Montana. They rise abruptly out of the Great plains, which have 

 an altitude of 4,000 to 5,000 feet, to altitudes which range from 10,000 to 

 slightly over 13,000 feet in the higher mountain summits. The portion 

 of the range to which the term Bighorn mountains is applied trends north- 

 northwest in the northern portion of its course and nearly due north and 

 south in the southern portion, where it joins a high east-west range 

 known as the Bridger range and Owl Creek mountains. 



The Bighorn mountains end at the north at the canyon of Bighorn 

 river, beyond which the same uplift is continued in the Pryor mountains, 

 a range of moderate elevation, which extends but a short distance. West 

 of the Bighorn mountains there is a wide area of plains known as the 

 Bighorn basin, which extends to the foot of the Shoshone mountains on 

 the west and the Bridger range and the Owl Creek mountains on the 

 south. 



STRUCTURE 



The Bighorn mountains are due to a great anticline of many thousands 

 of feet uplift, which has brought a thick series of Paleozoic and Mesozoic 

 sedimentary rocks high above the adjoining Great plains. Owing to the 

 deep erosion of the crest of this uplift, the mountains present a central 

 nucleus of pre-Cambrian granites, with the sedimentary rocks on the 

 flanks of the mountains and constituting plateaus at either end. The 

 region is one of exceptionally fine exposures, which afford a rare oppor- 

 tunity for study of the stratigraphic relations and variations. Most of 

 the rocks are hard, and streams flowing out of the central mountain area 

 have cut deep canyons and gorges, in the walls of which the formations 



t Bull. Geol. Soc. Am., vol. 3, pp. 153-172, pis. 3 and 5. 



