I08 THE JOURNAL OF GEOLOGY. 



tion than with reports of state or national surveys. At present, how- 

 ever, the more active state surveys oi^er the best approach to work of 

 this class, and with the recently increasing interest in physiographical 

 investigation, I hope to see chapters of their annual reports devoted to 

 well illustrated essays of this character.' 



Riigen, a composite island on the Baltic coast of Prussia, has long 

 attracted attention of geologists from the peculiar dislocations of its 

 Cretaceous strata, in which glacial till was peculiarly involved ; so that 

 some observers concluded the dislocations were the product of pressure 

 from the advancing ice sheet. Credner now concludes in effect as 

 follows : The Cretaceous strata, while still horizontal, were overspread 

 by a sheet of till. The compound mass was then, after the disappear- 

 ance of the ice sheet, fractured and dislocated in a rather irregular 

 manner, although the lines of movement in a measure follow systematic 

 courses. A new constructional topography was thus produced ; and a 

 significant advance was made in its subaerial denudation. Then a 

 second ice sheet crossed the Baltic, rubbed over the uneven surface of 

 Riigen, softened its surface expression, and distributed an irregular 

 deposit of drift over the Cretaceous beds and the older drift. Since 

 then, a moderate depression has submerged part of the region, convert- 

 ing Riigen into a group of islands ; and these have been in still later 

 times soldered together by sand bars. 



Concerning the evidence thus gained of a complex glacial period, 

 Credner remarks : A convincing proof of the long interval between 

 the two glaciations is found both in the heavy fracturing and faulting 

 that took place between the deposition of the two northern drift forma- 

 tions ; and in the distinct denudation that was suffered by the construc- 

 tional forms produced by the dislocations, before the deposition of the 

 second drift (p. 416, 417). 



W. M. Davis. 



' See The Improvement of Geographical Teaching, Nat. Geogr. Magazine, IV., 

 1893, 74- 



