May 29, 1896.] 



SCIENCE. 



797 



scores in breadth, and scores or hundreds 

 of feet in depth to the bottom of later lin- 

 ings, excavated chiefly in nonlithified de- 

 posits; in the interior area it is recorded in 

 steep-blufled canyons carrying all the rivers 

 and all but the smallest streamlets, exca- 

 vated in hard rocks ; and the two records 

 are not only consistent in kind and amount, 

 but intergrade in such manner as to estab- 

 lish substantial identity. In the glaciated 

 area the drift mantles a surface, which, so 

 far as outcrops and borings indicate, is the 

 counterpart of that found in the extra-gla- 

 cial region, e.g., in Ohio and western Penn- 

 sylvania numerous ancient drift-filled chan- 

 nels have long been known; in Indiana and 

 Illinois many such canyons have been re- 

 vealed by borings; in Iowa several have 

 been recognized for years and others have 

 recently been brought to light through the 

 researches of the State Survey ; indeed 

 throughout most of the glaciated region 

 such buried canyons are known. Now it 

 is noteworthy that all of these drift-filled 

 gorges thus far brought to light are consis- 

 tent in depth and width among each other, 

 and also with the gorges of the Mississippi, 

 Missouri and Ohio, not only inside the gla- 

 cial boundary, but outside that limit where 

 they form trustworthy records of the Ozar- 

 kian epoch. It is no less noteworthy that 

 Salisbury and others have detected remnant 

 gravel deposits, presumptively represent- 

 ing the Lafayette, far within the glacial 

 boundary; and the combined records of ag- 

 gradation and degradation indicate with con- 

 siderable clearness that the continental os- 

 cillations of the Lafayette-Ozarkian time 

 affected most or all of what is now the east- 

 ern half of the United States. This corre- 

 lation of degradation records without and 

 within the glacial boundary explains simply 

 and readily the peculiar configuration of the 

 pre-glacial surface which has puzzled many 

 students ; and at the same time it empha- 

 sizes the strong distinction between agen- 



cies and conditions of the two periods— the 

 Ozarkian epoch of high level and rapid deg- 

 radation, and the Kansan and succeeding 

 epochs of low altitude and aggradation or 

 feeble degradation. 



' In considering the physical history of the 

 southeastern quarter of the continent during 

 neozoic time it should be borne in mind 

 that there were two and only two great 

 eons or cycles of earth movement. The 

 first eon began with the profound oscillia- 

 tions attending the deposition and subse- 

 quent degradation of the Potomac forma- 

 tion, continued with ever-lessening ampli- 

 tude of oscillation nearly to the end of the 

 Tertiary, and closed with the remarkable 

 epoch of stability in the earth crust ante- 

 dating the Lafayette; the second eon be- 

 gan with the profound oscillation by which 

 the deposition and subsequent degradation 

 of the Lafayette were produced, continued 

 with diminishing vigor and amplitude of 

 movement to the end of glacial time, and is 

 apparently not yet closed, i. e., each cycle 

 began with strong movement which gradu- 

 ally declined and died away, the first in a 

 long epoch of quiescence, the second in the 

 gentle oscillation apparently in progress 

 to-day. It may be noted in passing that 

 there is a certain logical symmetry and 

 completeness in correlating these eons or 

 cycles with the stratigraphic and paleonto- 

 logic series, and thereby in referring the 

 second wholly to Pleistocene ; but it should 

 not be forgotten that there is no indubitable 

 evidence connecting the Lafayette with 

 glacial action, and a vast body of trust- 

 worthy evidence pointing in the opposite 

 du'ection, so that the logic of fact runs 

 counter to the logic of idea ; moreover such 

 a correlation tends to deepen the slough of 

 baseless speculation concerning the cause of 

 glaciation which alone seems to connect the 

 Lafayette with the glacial deposits. !N"ow 

 on considering in detail the oscillations of 

 the two eons, it is found that they run in 



