JURASSIC CYCADS FROM THE BLACK HILLS. 205 



FIELD NOTES. 

 By G. R. WiELAND. 



A comparison of the beds on the southwest side of the Black Hills 

 with those on the east and northeast sides shows that in the former 

 the beds lie nearly horizontal and are deeply cut by streams, so that 

 the linear exposure of the Jurassic is immensely increased. The most 

 marked change is in the diminution of the sandstone bed beneath the 

 main Atlantosaurus beds, or Beulah shale, if, indeed, the 25 feet of 

 yellowish sandstone here intervening between this bed and the marine 

 Jurassic may be considered equivalent to the "Unkpapa" of the east- 

 ern hills. And, conversely, there is an increased thickness of the over- 

 lying Beulah shales. Thickest on the northwestern side of the hills, 

 and absent from nearly opposite Hermosa to Minnekahta, this bed, 

 teeming at its base with the remains of huge dinosaurs, incloses the 

 Black HiUs like a long-armed crescent or horseshoe. 



Most unfortunately these saurian bones are seldom well preserved 

 and the collector is always baffled by one long stretch of talus after 

 another. It will prove possible, however, in the course of time, to deter- 

 mine the extensive fauna represented, and in part its silicified flora 

 of cycads and conifers. This being, of course, an easterly extension 

 of the Jurassic so well marked farther west, most of the forms are doubt- 

 less already known. The section is of especial interest in connection 

 with the stratigraphic relations of Cycadeoidea and Cycadella. 



Section 4 miles west ofHuleit, Crook County, Wyo. 



Feet 

 7. Various clays or shales and sandstones containing some silicified wood, and doubtless in their lower por- 

 tions the equivalent of the Blackhawk and Minnekahta cj'cad beds (overlain unconformably by the 



Fort Benton Cretaceous) _ 200 



S. Black S'hales containing more or less distinct remains of dinosaurs ■ 50 



5. Bluish shale weathering white. Contains remains of large dinosaurs, seldom well preserved, silicified 



wood, and probably cycads J2 



4. Yellowish to red shale _ g 



3. Clay containing three or four thin nodular layers with remains of large dinosaurs, and ending rather 



sharply below as light sandy or nodular material ^g 



2. Sharply defined stratum of yellowish sandrock, barren, so far as observed 25 



1. Marine Jurassic, ending above in limestone weathering whitish and containing remains of Baptanodon 



(and Megalosaurus?) 200 



Total (approximate). 535 



