1868.] 383 LMiller. 



to 20 feet across. This is a hard, tabulated sand-rock of a 

 dark color, with a shade of greeu in it, and apparently con- 

 tains some lime. The stem is a dirty white sand-rock, very 

 soft and friable. It is easily cnt with a pocket-knife, and can 

 be crumbled in the hands. There is a hole at the top of the 

 stem, shown in the picture, through which a child might creep. 

 The rocks here lie nearly horizontal, and the two strata, 

 forming the cap and stem, are re(/u!arlt/ in place in the " Mush- 

 room Rock." The valley in which it stands has been formed 

 by the rush of water, which has left here and there small islands 

 of the soft sand-rock, capped by portions of the hard stratum 

 above it ; and the running water first, and the rain, hail, and 

 dust storms of the Plains afterwards, have eroded the lower 

 stratum gradually, until at length the cap projected so far as 

 to protect the stem like an umbrella. 



There is danger that this strange monument of nature's 

 slow and curious working, and which has so long resisted the 

 elements, may perish in a most inglorious manner, unless 

 measures are adopted for its protection. Almost every visitor 

 is smitten with the American propensity for immortality, which 

 he indulges by inscribing his name on the yielding stem with 

 his jack-lviiife. Mea culpa, I confess to have done the same. 

 It is b}" no means impossible that the "Mushroom Rock" will 

 be thus whittled away, and the last Vandal may be caught in a 

 trap when it falls. 



A few hundred feet off there is another mushroom rock, 

 taller than that shown in our picture, but not so striking in 

 appearance, because the cap is smaller. There have been 

 several others in the vicinity, I believe. On the left side of 

 the picture the cap of one of them, which has fallen, may be 

 seen, and there are others of a like character around. 



I have only to add to this, upon the authority of Dr. Le 

 Conte, that these strata belong to No. 1 Lower Cretaceous 

 Group, according to the classification of Meek and Hayden. 



To the same formation belongs the " Inscription Rock," and 

 the figures upon it are inscribed on the same soft friable sand- 

 stone which forms the stem of the " Mushroom Rock." In 

 the admirable series of five photographs accompanying this 

 memoir, will be found a general view of this rock, and four 

 views of ditferent portions on a larger scale, showing the in- 

 scriptions, I will not call them hieroglyphics. While a very 



