﻿284 AMERICAN FOSSIL CYCADS. 



mile wide. It is from 100 to 125 meters deep, but its existence is not indicated on the 

 contour map of the U. S. Geological Survey. The base of the valley is mostly marine 

 Jurassic (Baptanodon beds), but in places, as at T, the Trias is exposed. 



Photograph 3. — Summit of high bluff at northern end of the Cycad Valley, with large 

 cycadean trunk (T. 208, figure 44) raised from its in situ original position. This location 

 is of especial interest because the large trunk here found can have been displaced but little 

 or not at all during erosion. (Cf. 178, p. 564.) The horizon is identically the same as that 

 of the Cycad Hill specimens 2 miles south. 



Plate L,. Upper and Lower Cycad-yielding Strata of Eastern Black Hills Rim, 

 near Piedmont, South Dakota, in the Piedmont Black Hawk region. 



Photograph 1. — Upper horizon. Straticulate sandstones forming Goblin Arch at the 

 northern border of the Cycad Valley, about 125 meters west of the cycad locality shown in 

 preceding photograph, plate xlix. The top of the arch marks the lower limit of the cycad- 

 bearing stratum, which consists at this point in deeply iron-stained to light flesh-colored 

 sandstone, and is succeeded by a heavy capping of quartzitic sand rock belonging to the 

 Dakota Cretaceous of Meek and Hayden. In the latter stratum but little silicified wood 

 occurs, while in the stratum beneath immense silicified Araucarioxylon logs are associated 

 with the cycads. A few hundred feet from the Goblin Arch the smaller end only of a 

 long section of an Araucarioxylon trunk 1 meter in diameter projects from its natural bed 

 of deeply iron-stained sandstone. This is essentially the same horizon as that which yields 

 the cycads of the old locality at the southern end of the Cycad Valley, where, however, 

 there is rather less iron staining. The evident continuation of the beds at the summit 

 of the Cycad Hill around to the northern end of the valley led the writer to the repeated 

 and persistent search which resulted in the discovery of the splendid trunk No. 208 (cf. 

 figure 44) at the point shown in the preceding photograph. It is also of interest to note 

 that the writer has secured cycad trunks in situ from both straticulate sand rock of nearly 

 similar character and much iron-stained sandstone superimposed, at Minnekahta, in the 

 Southern Black Hills, 60 miles southwest of the Cycad Valley. The relations are evidently 

 alike in both these localities. 



Photograph 2. — Lozver cycad-bearing horizon of the Black Hills Rim, as seen 1V2 

 miles east of Piedmont at the quarry made by the writer to secure the type specimen 

 of the huge Dinosaurian Barosaurus lentus Marsh. This lower horizon consists mainly in 

 dark or chocolate-colored to lighter and arenaceous clays, extending around the entire Black 

 Hills Rim, except for a few miles on the southeast. In it the trunks of the genus CycadeUa 

 occur rarely, associated with more frequent silicified wood and the skeletons of Dinosauria 

 and turtles (cf. page 8). Various sandstone, with occasional clay strata, aggregating from 

 30 to 60 meters thick, intervene between the lower and upper Black Hills cycad horizons. 



