Aviculopecten sp. 

 Cyathophyllum ep. 



382 INDEX TO THE STRATIGEAPHY OF NOETH AMEEICA. 



much less than normal thickness, the Quadrant is only about 50 feet thick. The usual thickness 

 is nearer the maximum than the minimum. 



Fossils have been collected from the lower member of the Quadrant formation at two locali- 

 ties in the Philipsburg quadrangle. Two miles south of Georgetown Lake the red shales below 

 the quartzite have yielded the following forms, identified by Dr. Girty : 



Archseocidaris ep. Productus cora. 



Fenestella sp. Spirifer rockymontanus. 



Rhombopora sp. Euomphalus catilloides. 

 Derbya crassa. 



Dr. Girty considers this faunule referable to the Pennsylvanian. 



The upper member of the Quadrant, in the Rock Creek section, is a single massive stratum 

 of pure hard quartzite about 300 feet thick. Almost everywhere else in the quadrangle it com- 

 prises (1) a basal stratum of pure vitreous quartzite; (2) a medial stratuim, generally not well 

 exposed, of calcareous shale, shaly and cherty limestone, and a peculiar cherty quartzite with 

 irregular limestone concretions; (3) an upper quartzite, less pure than the lower. The aggre- 

 gate thickness of these is about 400 feet on the little hill just west of the Philipsburg high school. 



Fossils collected at this place from the medial calcareous bed (2), were reported by Mr. 

 Weed in 1900." Girty referred these to the following forms: 



Camarotcecbia sappho. 

 C. near C. congregata. 

 Glyptodesma rectum? 



These fossils, in Girty's opinion, had a Devonian aspect. 



In 1906 D. F. MacDonald gathered at the same place a small collection, even less satisfac- 

 tory than Weed's. This was submitted to E. M. Kindle, who, although unaware of Girty's 

 report, hkewise hesitatingly referred the horizon to the Devonian. 



In the light of later evidence Girty has further discussed this fauna as follows : * 



"The fauna of lot 1 is with little question the same which Mr. Weed obtained from nearly 

 the same locality and which I reported on in 1900. 



"Although when I first encountered this fauna I referred it to the Devonian, I now believe 

 that it is probably Pennsylvanian. The two most significant types are the Camarotcechias and 

 the Glyptodesma rectum? Large EhynchoneUas are rare in the typical Pennsylvanian, and 

 none are known having the structure of Camarotcechia, as is the case with these. An exception 

 must be made of Rhynchopora, but that genus has also a punctate shell. It was largely on tliis 

 account, since Camarotcechia appeared to be restricted to the Devonian and Mississippian, that 

 I was previously led to determiae the horizon as Devonian. The force of this evidence holds 

 good to-day, more or less. On the other hand, the Glyptodesma rectum?, represented only by 

 one external mold, is probably a Myahna related to M. deltoidea Gabb. In view of the facts that 

 there has recently come to hand a large species of Camarotcechia (distinct, however, from the 

 Philipsburg forms) from Utah high in the Pennsylvanian and that the stratigraphic position of 

 lot 1 is above that of lot 12, it now seems probable that the age of the former is, as already 

 stated, really Peimsylvanian. In this event the fauna is unusual and interesting." 



H. S. Gale " in 1910 examined beds belonging to the Quadrant formation in the area south 

 of the Philipsburg quadrangle. He considers the lower and purer quartzite of the quartzite 

 member of the Quadrant equivalent to the Weber quartzite of southern Idaho and Utah, and 

 the portion of the formation above this quartzite as equivalent to the Park City formation of the 

 same regions. This correlation is based on lithologic similarity and the presence of phosphate, 

 which was found at the top of the cherty limestone between the two siliceou.5 strata. 



o Weed, W. H., Geology of the Little Belt Mountains, Montana: Twentieth Ann. Rept. U. S. Geol. Survey, pt. 3, 

 1899, p. 188. 



6 Personal communication. See also Kindle, E. M., Fauna and stratigraphy of the Jefferson limestone in the 

 northern Rocky Mountain region: Ani. Paleontology, Bull. Cornell Univ. No. 20, 1908, p. 19, footnote. 



"Oral communication to F. C. Calkins. 



