318 :MKS0Z()1C l-'LOKAS OF UMTED STATES. 



important foi-nis which may perhaps not be duplicated in a century are 

 collected and described with but the most imperfect record of their 

 locality and horizon. The accurate topographical and geological maps 

 now l)eing prepared will render this less and less likely to happen. In this 

 connection I should say that Prof. Henry F. Osborn, of the American 

 Museum of Natural History, throughout his extensive explorations in the 

 Rocky IMountain country has insisted upon the value of the vertical 

 record from the evolutionary point of view, and these notes have been in 

 large part prepared while engaged in field work for the American IMuseum. 



The general character of the sedimentary rocks of the Black Hills is 

 well knowri — the high outer rim of fossil-bearing Jurassic and Cretaceous 

 horizons, with the intervening eroded red Trias (or, as now seems more 

 probable, Permian) valley extending entirely around the central mountain 

 area of eruptive followed by Paleozoic rocks. I shall, then, at once give 

 certain sections, not onl_y of importance in the correlation of the "rim" 

 horizons as they extend around the hills, because well marked l:)y char- 

 acteristic fossils, but also because of the great biologic interest of thefaunal 

 and floral relations here seen. 



Three miles due north of Piedmont, S. Dak., near the middle of the 

 eastern side of the Black Hills, there is a characteristic section of primary 

 interest. The small knoll near which it is taken may serve to name it. 



Section at the tSaiwian Knoll, rf miles due north of Piedmont, S. Dak. 



Foot. 



12. Fort Benton shales, with perhaps 100 feet of underlying §trata not studied 129 



11. Massive more or less cross-bedded sand rock, flesh colored, barren (?), and here forniini; the summit 



of the riiu <iO 



10. Deeply iron-stained sandstone with much silicilied wood, doubtless equivalent to the cycad-bearing 



horizon east of Piedmont, and at least in part to that of Minnekahta 20 



9. Shale, gray to blue, with silicified wood 20 



8. White soft sandstone 10 



7. Sand rock, dirty white, granular, and containing Camptosaurus and other dinosaurs 2 



6. An all-shale talus CO 



5. Sand rock with two harder ledges ; 20 



4. Shale and limestone layers containing numerous ostracods and occasionally lish teetli (Hybodus >). . 20 



3. Prominent slialc bed, from base of which Barosaurus, Morosaunis, and other large dinosaurs weie 



collected, as well as much silicified wood HO 



2. Shale with nodular layers, containing more or less imperfect remains of numerous large saurians 20 



1. Drab to white sand rock, here much cross-bedded above (the Unkpapa of Darton ) 7.5 



Total 506 



Marine Jurassic. 



I should add that No. 3 is usually followed by light-colored sandstone 

 containing indistinct remains of plants. The.se i-arely become distinct. 



