80 The American Geologist. February, 1894 
acres about four or five miles south weal of Minnekahta. They 
all lay. partly imbedded in the soil, on the southern slope of 
one of the low. rounded, grassy hills that characterize the 
marginal portion of the Black Hills uplift. Separating the 
cycad hill from the next on the south is a •comparatively shal- 
low but steep-sided canon, supporting a comparatively dense 
growth of Pinvs ponder osa Douglas. The walls of the canon 
reveal the edges of gently folded and tilted beds of sandstone. 
Sandstones — yellow, brown, or red, sometimes in massive and 
sometimes in thinner layers — often project above the grassy 
surface on the gentler slopes above the canon walls; while 
here and there are high buttes, rising two or three hundred 
feet above the general level, and composed of conformable beds 
of sandstone throughout their entire elevation. A single sand- 
stone formation, therefore, extends from the bottom of the 
small secondary canons of the region to the top of the buttes. 
and. though no cycads were seen in place, there is no reason 
to doubt that it was in this sandstone, at some level, that they 
were originally imbedded. The sandstone exhibits the char- 
acteristics of the Dakota group of the Black Hills as described 
by Hayden, Winchell and Newton, still it was thought best 
not to decide the question of its age on lithological grounds 
alone. Diligent search during the short time at our disposal 
failed to disclose the remains of recognizable plants or ani- 
mals, belonging to the sandstone, in place. Fragments of si- 
licified trunks, probably of deciduous trees, lay loose on the 
surface. Some of these were mingled with the cycad trunks, 
and. since the condition of mineralization was tin- same in 
both, it was inferred that the silicitied trunks of both types 
had been imbedded under the same conditions and that they 
probably came from the same horizon. A short distance east 
of the cycad held a gray shale, supposed to be the .Jurassic of 
the geologists who have written on the Black Hills, was re- 
vealed by an upward arching fold in the bottom of the canon 
but. as it contained no fossils, judgment was for the time re- 
served. Three or four miles west of the main group of cycads 
ash-colored shales, recognized beyond a doubt by Belemnites 
densus and other characteristic fossils as the Black Hills "Ju- 
rassic," are exposed in full force in the east side of Big Horn 
basin. The whole thickness of the Jurassic, two hundred feet 
