428 Anxals of the Carnegie Museum. 



DAKOTA ? 



In several places beside those mapped by the United States Geo- 

 logical Survey, I have observed limestones containing non-marine 

 mollusca lying between Jurassic and upper Cretaceous strata. These 

 are well exposed on the lower Bighole River north of Zeigler's 

 Canon, in the Frying-Pan Iksin northwest of Dillon, on the west 

 slope of the Tobacco Root Range, etc. A small collection of the 

 fossils from Zeigler's Canon was sent to Professor Stanton. The 

 following is his report : 



Field No. 131, north side of Bighole, southeast of McCarty's 

 Mountain above Zeigler's Canon, Montana. 



Unio sp. Slender form of the type of U. douglassi. 



Corbula sp. Very abundant. Doubtfully referred to Corbula. 



Possibly two species. 

 Goniobasis ? sp. Very slender, smooth form. 

 Goiiiobasis increbescens Stanton. 

 Viviparus ? sp. 

 " This collection is from the horizon probably doubtfully referred 

 to the Dakota in the Yellowstone region. Its age is very doubtful." 

 Field No. 132. — From a higher horizon at same locality as 131. 

 Unio sp. Differs from one in lot 131. 

 Goniobasis ? increbescens Stanton. 

 Fish teeth, etc. 

 "This lot probably belongs to the same horizon as 131." 



Description of Plate. 



A-B. A Palaeozoic section on Camp Creek east of Melrose, Montana. The sec- 

 tion extends from ^ down the creek south of west to B, where Carboniferous lime- 

 stones form the western flank of the mountains along the Bighole valley. 



C-D. A section about fifteen miles to the southward of A-B and a little farther 

 east. This is nearly supplementary to the Camp Creek section, though there are un- 

 doubtedly some strata lost between the two. 



This section extends from above Zeigler's Springs up the Bighole from east to 

 west. It begins with heavy Carboniferous quartzyte. The upper portion of the 

 quartzytes contain Upper Carboniferous fossils. This is succeeded by Permian ?, 

 possibly Triassic, Jurassic and then Cretaceous strata. Then by a fault the Carbon- 

 iferous quartzytes come in again, overlying the Mesozoic and dipping at the same 

 angle. Above this the strata are repeated and continue up through Cretaceous to 

 Laramie and ending in McCarty's Mountain in what may be Livingston or later. 



This region presents a most beautiful study in dynamic geology, as the strata are so 

 plainly exposed. A mile north of here the section would be quite different. 



