International Excursion in America. 
37 
including one to the top of Pike’s Peak (14,109 feet) and another 
(2 days) to the top of Mount Garfield (12,365 feet). The opportunity 
thus afforded of studying the vegetation of this region in a more or 
less leisurely way, and the restfulness of the comparatively prolonged 
sojourn in so delightful a spot as Minnehaha, right in the midst of 
practically untouched forest and with a glorious view down the 
canyon over the Great Plains, were much appreciated by the party, 
who owe a special debt of gratitude to Professor and Mrs. Clements 
for their unwearying kindness and the great trouble taken to secure 
the comfort and convenience of all the members. During the stay 
at Minnehaha, Professor Engler of Berlin joined the party. 
The Rocky Mountains in the Pike’s Peak region are formed of 
Archaean granite weathering very easily into rough rounded frag¬ 
ments, largely ranging from 10 to 15 or 20 millimeters in diameter. 
This coarse gravel forms the very characteristic gravel slides which 
occupy many of the mountain slopes, and furnish the basis of the 
soil on which the succession to forest is developed. 
Minnehaha is situated in the Douglas fir (Pseudotsuga-mucronata) 
zone, and all stages of the succession from bare gravel-slide to 
Douglas forest may be studied in the immediate neighbourhood. 
These stages may be summarised as follows, according to Professor 
Clements: (1) Gravel-slide association with Aletes acaitlis, Brio - 
gonum flavuin, Mentzelia multiflora, Smilacina ( Vagnera) stellata, 
etc., forming an open (pioneer) association with large areas of bare 
gravel between the plants. This association begins to colonise the 
gravel-slide directly the downward movement of the slide is checked 
from any cause. The plants all have extensively developed under¬ 
ground parts which ramify in the gravel and by upward growth 
of the shoot-buds are able to keep pace with the movement of gravel 
from above which tends to cover them. (2) Half-gravel slide- 
association with Elymus triticoides (anibiguus) and Muhlenbergia 
gracilis largely covering the ground. Rubus deliciosus, Gilia 
aggvegala, Geranium ccespitosum and in places Yucca glauca are 
conspicuous species in this association. The half-gravel slide may 
be followed by (3) the thicket association, which may be regarded 
as the upward continuation of the chaparral which fringes the Great 
Plains. Indeed Quercus Gunnisonii is still found at this level, but 
dies out immediately above, and the thicket formation is here 
mainly composed of Holodiscus dumosus, Rubus deliciosus, and 
Opulaster opulifolia (monogyna), with Jamesia americana in 
company with the two last species extending to much higher 
