LAND AND SEA OSCILLATIONS ULRICH. 337 



nize two longer up warps of the Dresbach floor that extend in a south- 

 westerly direction from the central pre-Canibrian land mass which 

 formed the backbone of the Wisconsin peninsula. These buried 

 ridges divided the Franconia sea into basins sufficiently distinct to 

 show well-marked differences in their respective depositional sequen- 

 ces and faunas. 



But why pile up the evidence, the sameness of which must weary 

 you. Suffice it to say that the phenomena indicating differential ver- 

 tical displacements of the strand line are everywhere about us and as 

 abundant and well displayed in the areas of Paleozoic rocks as in 

 those of more recent ages. One need but to compare a series of 

 paleogeographic maps which, even despite their admittedly general- 

 ized and synthetic nature, yet show — unmistakably and clearly — 

 variations in outlines of successive continental seas that would have 

 been impossible if the land surfaces periodically invaded by them 

 had not been subject to frequent oscillation and warping. 



Physiographers, apparently, have paid little attention to these 

 paleogeographic maps and the discussions of stratigraphic corre- 

 lations that usually accompany them. Perhaps the reason for this 

 oversight lies in the fact that most of them have been made by pale- 

 ontologists — a kind of geologist who should be seen but not heard on 

 physiographic and diastrophic questions. But, after all, does not the 

 stratigraphical paleontologist deal with a wider range of geological 

 data and criteria than any other specialist in the science? Of them 

 all, I regard the stratigraphical paleontologist the best equipped to 

 bring out the dominant facts in questions of the kind before us. He 

 has the same opportunities and desires to observe and note the 

 physical factors of the problem, and in addition an appreciation of 

 organic criteria that may not only be applied directly in the field but 

 the tangible evidence — in the form of specimens usually small enough 

 to be collected — may be carried to the laboratory and there be studied 

 at leisure and as often as desired. I have found this of very great 

 advantage. 



For such reasons I would be disposed to prejudice in favor of earth 

 students like Vaughan or Schuchert in cases of controversy with 

 others who can not personally take into account and weigh the or- 

 ganic as well as the physical aspects of a problem. However, in the 

 present instance I have gathered so much competent evidence of my 

 own that I feel warranted in reaching the conviction that the major 

 factors in the control and migration of the strand line lie and have 

 always lain in deformative movements within the lithosphere. These 

 movements, whether large or small and whether due to shrinkage of 

 the centrosphere, to local changes in crustal density, to unequal load- 

 ing by rock or ice, or to erosion and further lightening of positive 

 areas, are all primarily concerned with the maintenance of isostasy. 

 42803°— 22 22 



