﻿97 Correlation 19 



feet below the top of the formation at Threeforks, which were 

 determined as follows: 



Spirifer disjuncta 



Chonetes macrostriata 



Smithiaf sp. undetermined 



Orthis sp. undetermined 



Concerning the several hundred feet below the horizon of this 

 fauna Peale was able to offer no evidence. 



Weed procured two small lots of corals in the Little Belt 

 Mountains 18 . One of these was reported by Schuchert to contain 

 Diphyphyllum ccespitosum Hall, which was regarded by him to 

 represent a Silurian horizon. The other lot, which Girty con- 

 sidered of Devonian age, contained Stromatopora, Pachyphyllum 

 (near woodmani H. & W.) and AcervuLaria. 



Considering the poor state of preservation of the corals as^ 

 generally found in this formation, the conflicting opinions based 

 on this class of fossils are not surprising. 



Weed 19 also records Girty 's report on a collection of fossils from 

 Philipsburg which is said to be of Devonian age. Through the 

 courtesy of Dr. Girty an interpretation of this faunule which is no 

 doubt the correct one is given in a note'below. This report seems 

 to be responsible for Weed's statement that the Jefferson lime- 

 stone locally grades into quartzite and sandstone. No cases of 

 such grading have been observed by the present writer. The 

 quartzite at Philipsburg, referred to by Weed, from which the 

 fossils came has been examined by the writer, who agrees with 

 Mr. Calkins that it represents a Carboniferous horizon appar- 

 ently identical with the Quadrant. 



From the foregoing it will be seen that the published data 

 regarding the age of the Jefferson limestone are very scanty and 

 by no means conclusive. 



'Twentieth Ann. Rept. U. S. Geol. Survey, pt. 3, 1900, p. 288. 

 ''Twentieth Ann. Rept. U. S. Geol. Survey, pt. 3, 1900, p. 288. 



Note. I avail myself of this opportunity to correct an error which I 

 made eight years ago in identifying as Devonian a small lot of fossils from 



