18 abstracts: geology 



value, as it offers to the engineer and map maker a large number of 

 points determined trigonometrically and correlated on one geodetic 

 datum. These stations or points are a part of a framework, composed 

 of the connected triangulation of the country, from which the state, 

 county or private surveyor may extend triangulation of a lower grade 

 for the control of detailed work. A. L. B. 



GEOLOGY. — The Pleistocene of Indiana and Michigan and the history 

 of the Great Lakes. Frank Leverett and F. B. Taylor. U. S. 

 Geological Survey Monograph 53. Pp. 529, maps and illustrations. 

 1915. 



This monograph describes the glacial features of Indiana and the 

 southern peninsula of Michigan and the great glacial lakes which bor- 

 dered the receding ice front. Brief mention is also made of related 

 glacial and lake features in Ohio, New York, Ontario and Wisconsin. 



Glacial drift of Illinoian age extends 50 to 100 miles south of the 

 border of the Wisconsin drift in Indiana and probably underlies the 

 whole extent of the Wisconsin drift in the area described. Till of pre- 

 Wisconsin age has been penetrated by borings over considerable areas 

 in the Saginaw valley. 



At its maximum extension the Wisconsin ice sheet was not very 

 definitely lobate but by the time the recession of the ice margin had 

 progressed 75 to 100 miles the Huron-Erie lobe on the east began to be 

 sharply separated from the Lake Michigan lobe on the west and a well 

 defined reentrant appeared between them. Terminating at first in 

 northern Indiana, this reentrant rapidly widened and extended north- 

 eastward into Michigan until the Saginaw lobe became a distinct 

 feature. All three of the ice lobes retreated in an oscillating manner 

 and made a series of moraines. Readvances appear generally to have 

 been relatively small, but in one or two cases they amounted to at least 

 20 to 25 miles. 



The report deals at length with the development and relations of 

 the three lobes and their effects on drainage and on the great lakes 

 which gathered in the great valleys whose natural outlets were tempor- 

 arily obstructed by the ice. 



Among the moraines the Port Huron morainic system is particularly 

 well marked, being identifiable from eastern Wisconsin to western New 

 York. This system appears to mark a longer step of retreat and read- 

 vance than the average. During a later stage drumlins were formed 

 over a considerable area around Charlevoix, Michigan, and a few in 

 other places. 



