318 MESOZOIC FLORAS OF UNITED STATES. 



important forms which may perhaps not be duphcated in a centurj^ are 

 collected and described with but the most imperfect record of their 

 locality and horizon. The accurate topographical and geological maps 

 now being 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 Mountain 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 Museum. 



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

 well known — 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 only of importance in the correlation of the "rim" 

 horizons as they extend around the hills, because well marked by char- 

 acteristic fossils, but also because of the gz'eat 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 Saurian Knoll, 3 miles due north of Piedmont, S. Dak. 



Peet. 



12. Fort BeQtoa shaleg, with perhaps 100 feet of underlying strata not studied 129 



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



of the rim 60 



10. Deeply iron-stained sandstone with much silicified wood, doubtless equivalent to the cj'cad-bearing 



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



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



8. White soft sandstone T • , . 10 



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



6. An all-shale talus. 60 



5. Sand rock with two harder ledges 20 



4. Shale and limestone laj'ers containing numerous ostracods and occasionally fish teeth (Hybodus ?). . 20 

 3. Prominent shale bed, from base of which Barosaurus, Morosaurus, and other large dinosaurs were 



collected, as well as much silicified wood 60 



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



1 . Drab to white sand rock, here much cross-bedded above (the Unkpapa of Darton ) : 75 



Total ^ : 506 



Marine Jurassic. 



I should add that No. 3 is usuall}^ followed bj^ light-colored sandstone 

 containing indistinct remains of plants. These rarely become distinct. 



