118 FIELD CoLUMBIAN MusEuM—GEOLOGY, VOL. 1. 
INFERENCES REGARDING CLIMATE. From the evidences of 
earlier extension of the glacier beyond its present limits, certain infer- 
ences regarding former conditions of climate can be drawn which, 
while by no means positive, are at least pertinent. In the first place, 
the difference in size and distinctness in origin of the two older 
lateral moraines, indicates remarkable variations in climate as regards 
temperature or snow fall. 
The conditions which produced these, could not have been those 
of gradual, constant return to a warmer climate, but rather a varying 
return, marked either by sudden renewal of former conditions, or by 
cyclical movements, the climax in cold or precipitation of which is 
represented by each moraine. The gap between the greatest extent 
of the glacier and the oldest lateral moraine, between this moraine 
and the younger one adjoining and between the latter and the present 
glacier limits points to a similar conclusion. It is easy to go farther 
and inquire whether the greatest extent of the glacier was not con- 
temporaneous with the Glacial Period, and, therefore, that a lowering 
of temperature at that time for the whole globe, is indicated. As is 
well known, observations hitherto made in the Andes and Himalayas 
point to such a conclusion. It is interesting, therefore, to find that 
the evidence here corroborates such a view. 
Before leaving this subject mention should be made of the view 
of Packard* that the entire region shows marksof glaciation. Accord- 
ing to this author the mountains must have been covered with glaciers 
which descended to a point 9,000 feet above the sea, and about 1,000 
feet above the present level of the plains. The low, rounded hills at 
the base of Popocatepetl he regards as of moraine origin, and from 
this point he observed moraines as far upas the snowline. He infers 
that the ice must have filled the valley or pass between Ixtaccihuatl 
and Popocatepetl, spreading out over the plateau like a mer de glace 
and sending glaciers down to the lakes then covering the plains of 
Anahuac. 
While hesitating to differ from the opinion of so experienced an 
observer, I am unable to believe that evidences of so extensive glaci- 
ation as he reports can be found. So far as I could observe, there 
is no drift or moraine material to be seen on the lower slopes of either 
of the mountains. The absence of bowlders from the soil of these 
slopes is indeed remarkable, and indicates quite strongly that the soil 
is of stream and lake deposit in the lower slopes, while on the upper 
itis formed solely by the disintegration and decay of the underlying 
rocks. Almost the only bowlders to be observed in these regions are 
*OP. cit. p. 113. 
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