286 THE ROUND MOUNT. Book II. 
cleft, over the edges of which only the top of a few juniper- 
trees were seen, I rode straight toward the foot of the two 
domes — a general uprising of the prairie — until I saw at my 
feet the deep chasm in the rock, which cuts off all communi- 
cation with the other side. This fissure proves that the rise 
of the ground, which forms the basis of the two cones, has 
been caused by upheaval. The cones may have arisen 
in part (as is evidently the case with Hound Mound) from 
the heaping up of thrown-out masses, and at the same time 
streams of lava have overflowed the country around the 
point of eruption. 
We drove along the cleft for some distance, until it wore 
away and allowed us to cross to the other side. Here the 
ground was again higher, and we proceeded toward Bound 
Mount — another trap dome — which I ascended, whilst the 
caravan encamped at its foot. The mountain stands on a 
bladder-like rising of the ground (similar to the base of 
Babbit's Ears), whose upraising has caused another similar 
fissure. I could only see this latter from the top of the 
mount, at a distance. The base is all around strewn with 
red and brown scoria and small ejected pieces of lava and 
half-melted sandstone : it rises to a height of about eight 
hundred feet above the plain, consisting of strata of lava 
overlaying one another. The rocks of the summit were 
clothed with a thick covering of yellow lichens : on its 
sides I found a pretty little Liliacea, and the first speci- 
men of the Opuntia arborescens, a plant which in the north 
of Mexico is one of the natural features of the country. A 
small alpine-looking Artemisia, with grey felt-like leaves 
and of an exceedingly aromatic scent, formed great part of 
the vegetation on this cone : the grass of the prairie grew 
up the sides and to the top of the mountain. Here I was 
rewarded by a grand view. To the north-west rose the 
