446 GEOLOGY. 



the same may be said of the suggestion that glaciation was due to a 

 change in the prevailing direction of the winds. Some notable modi- 

 fications of the winds must probably be factors in any complete glacial 

 hypothesis, but the causes and conditions that determined these are 

 scarcely less problems than glaciation itself. While no theory is ulteri- 

 orly without dependence on unsolved factors, a theory of a geologic 

 phenomenon is relatively complete when it is carried back to the gen- 

 eral course of events that form geologic history, such as deformation, 

 geographic changes, or astronomic relations. 



Formations Outside the Ice-sheets. 



While the glaciation of middle and high latitudes was the most 

 striking event of the Quaternary period, by far the larger part of the 

 earth's surface was not affected directly by the ice. Outside the 

 area of glaciation, the commoner phases of erosion and deposition were 

 in progress, and non-glacial Pleistocene formations are wide-spread, 

 though by no means universal. Degradation in some places was the 

 antecedent of deposition in others, and under the varied conditions 

 of the period, various classes of deposits were made, among which 

 were the following: 



(1) Eolian deposits, conspicuous along many sea and lake shores, 

 along many rivers, and in sundry arid and semi-arid regions, and incon- 

 spicuous as a dust mantle in every lodgment area, for wind-blown dust 

 is essentially ubiquitous. (2) Fluviatile deposits were made (a) by 

 streams which had no direct connection with the ice, and (b) by those 

 which had such connection. These deposits occur along essentially 

 all streams of low gradient, and along many streams where the gradient 

 is not low. Kindred deposits were made by sheet-floods and tem- 

 porary streams, even far from the courses of permanent streams. They 

 are common at the bases of most slopes, where they are often more 

 or less mixed with talus. (3) Lacustrine deposits of both the glacial 

 and non-glacial types, comparable to the two classes of river deposits, 

 were formed not only in existing lakes and more or less generally 

 about their borders, but over the sites of the numerous lakes which 

 have become extinct since the beginning of the period. (4) Character- 

 istic deposits were made by springs. (5) Terrestrial organic deposits 

 (peat, calcareous marl, etc.) abound in many of the ponds and marshes 



