LETTER OF TRANSMITTAL. 



University of Chicago, July 15, 1898. 



Sir: I have the honor to transmit herewith the manuscript of a mono- 

 graph on The Illinois Glacial Lobe, by Mr. Frank Leverett. This is one 

 of a series of monographs which are in course of preparation on the glacial 

 formations of the Northern States. My instructions when entering upon 

 the work of the Geological Survey were to prepare a monograph on the 

 terminal moraines which stretch from Dakota to the Atlantic. Soon after 

 the inauguration of the work, however, it became apparent that the mo- 

 rainic systems were more amply and more intricately developed than had 

 been at first apprehended, and that they, together with the associated glacial 

 formations, were so highly diversified and so complicated that their eluci- 

 dation could be reached only by prolonged investigation involving detailed 

 work. It was therefore thought best to study the glaciated area by sec- 

 tions, and to publish the results of these partial studies as they might be 

 ready, reserving for a later date the monographic treatment of the whole. 

 Early in the preliminary work special attention was drawn to the Illinois 

 glacial lobe, because its morainic ridges and its till sheets were very widely 

 deployed and because its relations were such as to make it, in some sense, a 

 key to the whole glacial series east of the Mississippi; and hence it has been 

 given precedence. 



Previous to my connection with the Geological Survey I had made 

 sufficient reconnaissance of the area covered by this monograph to deter- 

 mine some of its salient features, and at the same time to disclose many 

 other features which only patient and detailed study could elucidate. The 

 results of these partial studies, combined with observations made during the 

 first year of my connection with the Survey, were embraced in a prelim- 

 inary paper published in the Third Annual Report. The more detailed 

 work was taken up by Prof. R. D. Salisbury, Prof. L. C. Wooster, Mr. Frank 



