Geological Causes of (he Scenery of Yellowstone Pavk. 163 
and finally the deep-ljnng basalt was pressed throngh the 
dykes. 
Nine-tenths of the park is composed of volcanic rocks and 
the scenery must necessarilj' be diiferent from that of regions 
composed of sedimentary rocks. The Appalachian system or 
that of the Alps, from which the majority of our people obtain 
their ideas of mountain scenery, contain no rock like this. 
The volcanic rocks of the park show no peaks, for example, 
like those in the Alps whore stratified and schistose rocks have 
been folded into sharp anticlines that by wearing away have 
left jagged peaks steep on all sides. The volcanic rocks hav- 
ing no pronounced parallel structure and never having been 
subjected to great pressure and contortion wear away on the 
surface in rounded forms and where carved by streams show 
pinnacles and crags whose mass is horizontal. Thus we see 
that the scenery of the park is the result of the material used 
in its construction as w'ell as the result of its newness and its 
surroundings. Now we may further see how it is the result 
of the destructive agents at work there. 
The periods of eruption were followed by an ice age in 
which glaciers covered the whole of the park and scoured it 
from one end to the other. As the volcanic rocks w'ere still 
hot in places the melting of the encroaching ice would be very 
rapid and the resulting floods enormous and very powerful in 
erosion. One glacier moved west from the Absarokas and 
another east from the Gallatins. They met in the vallej' of 
the Gardiner and moved north, carving out the valley of the 
Yellowstone along a line of faulting. Evidences of the gla- 
eiation are seen in the valleys which are strewn with scratched 
and rounded bowlders that have been carried long distances 
from their source. 
But a far more powerful and deep working agent than the 
ice is the chemical action which, as the result of water, heat, 
and subterranean gases united, has showed its power far and 
wide in an astonishing degree. Geysers and hot springs, ex- 
tensive decomposition and deposition and the wonderful col- 
ors of the region are illustrations. 
In no other place in the world can geysers be seen to such 
advantage. Those in Iceland, New Zealand and California 
are neither so accessible nor beautiful. Geysers, boiling springs. 
