POPOCATEPETL AND IXTACCIHUATL— FARRINGTON. 117 
‘ 
the drainage from both sides, and this naturally grows wider and 
deeper as long as the conditions remain the same. Thus a ridge of 
debris is piled up against the wall of the cliff, and its content is 
increased by every advance of the glacier. 
It is evident that when such a formation takes place on an open 
surface, a double slope will be formed and thus will be produced 
moraines of the form already described. | 
There can be little doubt that the terminal moraine which I have 
mentioned as extending across the valley, as well as the ridge to the 
south marked ‘‘moraine’”’in Pl. XIV, was contemporaneous in origin 
with one of these lateral moraines. The material of the former, 
however, has been largely removed by glacial streams, so that the 
entrance to the valley lies comparatively open at the present time. 
6. GLACIATED SURFACES ON THE MOUNTAIN SIDE. On the 
way up from the cave to the glacier, rock surfaces which plainly 
showed the marks of glacial action were everywhere in evidence. 
The first were seen about three miles below the glacier at the point 
indicated in Pl. XIV. From this point on they became more numerous 
and could be seen on every side. Projecting bosses of rock were 
smoothed, polished and striated on the sides and top, and the upper 
edges of nearly all the western escarpments were noticeably rounded, 
The strie did not have great depth, nor did the rounding of 
the escarpments indicate that they had been subjected to great pres- 
sure, yet the evidences that the region had been covered by a glacier 
were unmistakable. 
Just what was the extent of this glacier, I can not positively state. 
Upon Pl. XIV the point at which the first glaciated surfaces were 
noted is marked. Yet there were no evidences of drift at this point, 
nor in the vicinity.. The ridge from which the view, Pl. XIV, was 
taken is one rising quite sharply from the slope of the mountain and 
running in an east and west direction. 
If the glacier had extended below it, marks of glacial actionshould 
be left on the sides or top of the ridge. WhileI can not gay that 
there is none such, none was noticed. The rather gentle slope of 
the ridge forming to the north one side of the valley, in contrast to 
the steep, rugged character of the southern slope suggests, however, 
that the former might have been one side of the valley through which 
the glacier flowed. 
It may, therefore, be concluded that either the easy decomposa- 
bility of the rocks left by the glacier on its retreat has caused them 
all to disappear, or that the greatest extent of the glacier may be 
found at a point farther down the mountain side than was observed 
by the writer. 
