RHYTHMS l>s' DEM DATION 767 



Long inlei'N oiling periods of wanner climate seem to sliow tliat this is in 

 reality a converging series and not merely an effect of perspective, from 

 a point of view nnable to see the full record of the farther pa vt. 



Thus from the oscillations of climate, as well as from tlie signs of un- 

 rest in the crust, there is seen to he no evidence that the culmination of 

 the present period .of terrestrial revolution is past. The evidence is sug- 

 gestive, not definitive; but the indicatiojis. of tjie (juickening series are 

 tliat, although' at the geologic moment the crust is in a minor suhmergent 

 phase and the climate of interglacial charactei', yet the ciisis may be 

 before us, not behind us. Men have taken hope 1]iat tlie Ice Age is 

 past and have looked on the Quaternary revoiiition as closed ; but the 

 study of the rhythms robs us of that assurance. At several times in 

 the Pleistocene that view, as based upon apparent sul^^idences of crustal 

 and climatic movements, would have been far better justified liy the evi- 

 dence than it is at the present moment. The high latitudes, unlike their 

 state through the most of geologic time, are still mantled with glaciers. 

 The shorelines are now in a. stage of earliest youth. We live, in fact, 

 within the Age of Ice, within an age of crustal uni'cst and revolution; 

 the geologic morrow may bring forth greater and more conipelling change- 

 than the geologic yesterday. 



CONTRAST OF CENOZOW AXD PALEOZOIC COXTiNEXTAL RELIEPH 



The present mean elevation of the lands is approximately 2,400 feet, 

 and Murray, in 1912, places their area at 59,810,000 square miles. The 

 waters with a depth of less than GOO feet surrouiuh'ug the lands cover 

 10,000,000 square miles. Taking this area of shelf seas as part of the 

 continental platforms, the continents are now six-sevenths emerged. lieck- 

 oning in these margins does not, however, give a just eom])arison with the 

 attitude of the land-masses during the spread of epeiric seas. It 1^ rather 

 the continental interiors wliicli offer the more significant contrast. The 

 floor of the shelf seas forms the continental terrace, wliich is in consider- 

 able part the result of a sedimentary outbuilding. Suppose the sealevel 

 to sink 600 feet. If the movement were moderately sIo^a', the construc- 

 tion of a new but narro^Aer submerged shelf would keep pace with the 

 uplift. The unconsolidated deposits of the present shelf seas, exposed to 

 erosion by uplift, would be planed down with great rajiidity b}' river 

 action and wave action, new waste from the land would also be contrib- 

 uted, and thus a submerged shelf would be maintained. 



The present epeiric seas of north westerji Eurojie and northern !N"orth 

 America are not comparable in cause to the Paleozoic seas. The Baltic 

 and Xorth seas and Hudson F)av show a close relation to the lowlands 



