REPORT OF TEE CHIEF ASTRONOMER 111 



SESSIONAL PAPER No. 25a 



is nionoclinal, with an average northeasterly dip of about 45 degrees. The 

 apparent thickness of all the strata is approximately 1,600 feet. Of this total 

 300 feet represents dolomitic quartzite, occurring at the base of the section. 



The quartzite is white to cream-coloured on the fresh fracture, weathering 

 yellowish or buff. Its beds are generally thick and massive. It bears no observed 

 fossils other than a few markings like annelide borings. 



Conformably overlying the quartzite is the very massive limestone, which 

 rarely shows bedding planes. This rock is usually fetid or bituminous on the 

 fresh fracture. It weathers from the normal dark gray tint to a much lighter 

 one. Cherty nodules up to three or four inches in diameter, are common in 

 certain horizons. 



FOSSIL^. 



Just above the contact with the underlying quartzite a collection 

 of fossils, bearing the station number 1217 on its labels, was made. These 

 were determined by Dr. H. M. Ami, whore notes are here entered in full: — * 



' Station No. 1217. — Boundary monument at eastern edge of the Tobacco Plains. 

 In a dark gray, impure crinoidal and at times semi-crystalline limestone. 

 Age: Upper Devonian. 

 Formation: Jefferson limestone. 

 Genera and species: 



1. Crinoidal columns. 



2. Productella suhaculeata. 



3. Schizophoria striatula. 



4. Athyris vittata. 



5. Athyris vittata, a narrower and more tumid form. 



6. Athyris vittata, fimbriate form. 



7. Athyris parvula, Whiteaves, or allied species. 



8. Athyris aff. Colorado ensis, probably a new species. 



9. Athyris. 



10. Trematospira (?) sp. No species of this genus has as yet been 



obtained from these limestones in Montana. 



11. Pugnax pugnus, a small diminutive form. 



12. Spirifer whitneyi, compare Hall's Spirifer whitneyi (Spirifer 



animascensis) . 



13. Spirifer disjunctus, var. animascensis. A specimen with high 

 area and fine plication on the costae, high and twisted beak. 

 Resembles a form from S. W. Colorado. 



* Both the writer and Dr. Ami are under special obligation to Dr. G. H. Girty and 

 to Dr. E. M. Kindle of the United States Geological Survey for valuable aid in deter- 

 mining the material of these collections; also for excellent opportunities for Dr. Ami 

 to compare the Canadian forme with specimens from various localities south of the 

 International Boundary. 



