LAND AND SEA OSCILLATIONS — ULRICH. 329 



when some of the higher parts of the marginal lands were ice- 

 covered, in some instances attaining locally to glacial conditions. 

 Here and there regular tillites are indicated, notably as recently 

 brought out by Dr. Edwin Kirk, in the Silurian deposits along the 

 coast of Alaska. Occasionally, too, transportation of bulky erratics 

 by heavy shore ice is suggested, as, for instance, by the late Ordo- 

 vician Rysedorph hill conglomerate near Albany, New York, and 

 the great masses of unworn limestone of Ordovician and Silurian 

 ages found in the early Pennsylvanian Caney shale of eastern Okla- 

 homa. But the Paleozoic history of North America so far as known 

 affords no suggestion of ice ages comparable to the Pleistocene period 

 in the amount of water abstracted for the formation of the ice sheets. 

 Moreover, by far the majority of the displacements of the strand line 

 in the continental seas occurred at times and places that give no 

 indication whatever of particularly cool climates. On the contrary, 

 the entombed faunas in the overlapping and interfingering marine 

 formations could hardly have lived in the shallow seas if the climate 

 of the adjacent lands had not been mild. 



With the data in hand I feel warranted in asserting that the level 

 of the Paleozoic continental seas was seldom appreciably affected 

 and certainly never controlled by glaciation. Besides, the appar- 

 ently irregular, though doubtless rhythmic, shiftings of the strand 

 line almost without exception indicate local differential movement 

 in the continental surface. And these movements must have been 

 connected with other more general movements, requiring at times 

 partial or complete withdrawal of the waters from the land depres- 

 sions, at other times permitting readvance in the same or some other 

 newly depressed land basin. 



The varying distribution of marine deposits of successive ages 

 naturally suggests differential upward and downward movement of 

 the lands as the immediate cause. If the submergences had been 

 occasioned solely by rise of the waters, the successive submergences 

 would have been always similar in geographic pattern and different 

 only in lateral extent. In fact, a general similarity or repetition of 

 old patterns is recognizable, but there is also exceeding diversity of 

 expression, and often the difference is greatest when directly succeed- 

 ing stages are compared. Often, again, when one stage appears to 

 have been very different from the next, the following third or fourth 

 may be very much like the first. Only oscillatory movements or 

 warping of the land surfaces could prodiice such results. The area 

 affected by such movements may be very large, as, for instance, dur- 

 ing the Middle Ordovician and Middle Silurian, when nearly half of 

 the continent of North America was involved. During these periods 

 the Gulf waters seem at certain times to have been completely with- 

 drawn from the southern part of the continent, the middle and 



