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GLACIAL CLIMATE. 
TC. Moreins, Pa we 
APRIL 19, I9O1. 
One of the difficult questions that confronts the student of 
glacialogy to-day is to give a satisfactory explanation for the 
change in climate that would produce glaciation at low levels in 
northern United States. It might appear at first glance that the 
investigations of recent years which have added greatly to our 
knowledge of glacial phenomena would have simplified the ques- 
tion but such is not the case. The investigations have added addi- 
tional conditions to the problem in even greater proportion than 
positive information has been gained towards an answer. 
A few years ago it was only necessary to account for one 
glacial period, now he who would give an acceptable explanation 
must account for several, he knows not how many. Some of the 
leading glacialogists tell us that there were not less than five or 
six glacial periods in Pleistocene time while others contend that 
there was only one. Previous to the glacial period of Pleistocene 
time there were probably other periods of glaciation but it is not 
safe at the present time to say how many. It appears to be well 
established that there was a glacial period at or near the close of 
the Carboniferous age, which produced glaciers on both sides of 
the equator between 20 and 30 degrees. Between that period and 
this there was a mild climate in high latitudes during a consider- 
erable portion of Mesozoic time. More-over there are periods of 
aridity during Triassic, Permian and Silurian times that indi- 
cate great climatic changes that are probably more or less closely 
related to glacial climatic changes. 
Hence any explanation for the glacial climate that would not 
permit a number of recurrences would not be received with 
much favor by many of the glacial students. Quite a number of 
hypotheses have been advanced to account for the different cli- 
matic changes, some of which are purely speculative and some are 
based on sound principles and have been received with consider- 
able favor. While some of these explanations have been received 
