320 A. P. COLEMAN 
San Juan. The nearest point to the outcrops on the railway 
between San Juan and Mendoza is at Paradero, kilometer 489. 
The railway traverses a desert country covered with sand and stones 
with isolated hills of rock not far to the east and the loftier Chico 
de Zonda, a range of foothills of the Andes, about eight kilometers 
to the west, as shown on Stappenbeck’s geological map of the 
region. Walking westward over the desert from the railway there 
is a gentle rise for two or three kilometers, followed by low ridges 
between profound ravines, apparently cut by temporary streams 
due to cloud-bursts in the mountains. At about five kilometers 
west there are steeply tilted red shales dipping westward, followed 
by hills of a green, basic eruptive, greatly weathered, and then 
high cliffs of gray Immestone. In the latter rock, fragments of 
crinoids and a syphon of orthoceras were found. It is indicated 
on the map as Silurian. 
A little to the south of this section, where a narrow valley pene- 
trates rugged hills, a greenish-gray shaly or slaty rock occurs, 
crumbling to fine débris on the surface, and including one or two 
bands of dark-brown pebbles and larger stones (Fig. 2). Most of 
the stones are fairly well rounded, as if rolled on a beach or in a 
river, and many have been ‘broken and recemented. Frequently 
they have been broken again where they lie on the surface, probably 
by alternations of heat and cold. 
A number of these stones are striated, often on more than one 
face. The largest seen was half a meter or somewhat less in 
diameter and was strongly scored. The stones are mainly basic 
eruptives, quartzite or limestone, the last too much attacked to 
show marks of glaciation. These stones appear to have been 
imbedded in the weathered, shaly rock, and in a ravine near by 
a few isolated ones are found still inclosed. The series appears 
to be tilted, but the dip and the limits of the bowlder bed could 
not be sharply determined, and in places two bowlder beds occur 
separated by a few meters of shale. These outcrops of loose, 
striated stones were followed for nearly a kilometer in a southerly 
direction, running parallel to the strike of the rocks in the foothills. 
Somewhat to the southwest, where the narrow valley is steep- 
walled and approaches the cliffs, a side ravine disclosed an abso- 
