Douglass : A Geological Reconnaissance. 269 



in a former paper:'' but further observations of Stanton, Hatcher, and 

 myself enable me to now more fully describe and to more correctly 

 correlate some of the horizons. 



In the descriptions which follow, I shall first characterize each horizon 

 as it occurs in the Fish Creek region, when it is represented in that 

 section. 



Jurassic (?) 



Fish Creek Section. — The lower beds, which appear on the surface 

 in the region of Fish Creek, are hard quartzites in which no good fos- 

 sils were found. These are exposed in a dome-shaped uplift on the 

 ranch of Mr. Joe Widdecombe, about eight or ten miles southeast of 

 Harlowton, which is near the Musselshell River. The overlying rocks 

 have been removed by erosion and left the more or less massive quartzite 

 as a mound, or "hogback." This rock is much like the hard quartzites, 

 which in the Three Forks section are beneath the band of limestone 

 containing marine fossils, which were determined by Dr. P. E. Ray- 

 mond as of Jurassic age. This formation is referred only provisionally 

 to the Jurassic. The overlying red and somber clays contain bones 

 of large dinosaurs and fresh- water mollusca. I had supposed the 

 bones to be those of Jurassic dinosaurs, but, as these have not been 

 studied or their species determined, and as Professor Stanton has 

 studied the mollusca and believes the formation to be not lower than 

 Lower Cretaceous, I shall, in this paper, refer these beds provisionally 

 to that horizon. 



The Big Hole Section. — On the lower Big Hole River about fifteen 

 miles north and a little east of Dillon, is a Mesozoic section as finely 

 exposed for study as that on Fish Creek, but it extends much lower 

 in the geological scale. Unfortunately, however, characteristic fossils, 

 which will fix beyond doubt the exact geological levels of strata in 

 various portions of the section, have not been found, so the exact age 

 of all the Mesozoic horizons is more or less uncertain. I made detailed 

 measurements of the lower portion of the section, but the upper por- 

 tion, which probably includes strata representing part at least of the 

 Dakota, Montana, Colorado, Laramie, and possibly the Fort Union, 

 was not carefully studied. The measured section undoubtedly includes 

 the fresh-water Jurassic, the upper and lower limits of which are un- 

 known. It begins below with the Upper Carboniferous and includes 



'""' A Cretaceous and Lower Tertiary Section in South Central Montana.'' Proc. 

 Anter. Philos. Soc, Vol. XLI, No. 170, 1902. 



