50 GLACIAL FOKMATIONS OF ERIE AND OHIO BASINS. 



The studies upon which the present repoi't is based, as well as those of the 

 earlier report/ have developed evidence which, in connection with other 

 evidence gathered in various parts of the glacial field in this country and 

 in Europe, is thought to have a decisive bearing upon the question. The 

 evidences of prolonged intervals of deglaciation are strong and have been 

 decidedly increased by the progress of critical study. 



The several sheets of glacial drift in this and neighboring regions have 

 received geogi'aphic names, as have also some of the interglacial beds. 

 Names of this class were proposed by Chamberlin a few years since as a 

 substitute for the time phrases which had arisen and which were of contro- 

 verted application.'- As these naujes represent only the main divisions of 

 the Glacial epoch, others are necessary to denote the sabdi visions. In the 

 report on the Illinois glacial lobe, and in the present report, several names 

 are thus introduced to designate the moraines and their associated sheets of 

 drift. These names are usually selected from towns located on the moraines 

 or from streams whose courses are governed by the morahies. In most cases 

 they have come into use in the office and in correspondence with other gla- 

 cialists, as a convenient form of reference. The selection of names thus 

 made seems suitable for general use. 



The outline given below aims to cover the events between the deposi- 

 tion of the oldest recognized drift sheet and the final recession of the ice 

 sheet into the region north of the Great Lakes. The main divisions appear 

 to be much longer than the secondary ones. The latter are not thought to 

 be marked by intervals sufficiently prolonged to merit the application of 

 the term epoch. It is probable, however, as shown further on, that some 

 oscillations of the ice front occurred, so that the moraines on which these 

 subdivisions are based do not mark simply halts in the recession of the ice. 



outIjIKe of drift sheets and intervals. 



1. Oldest recognized drift sheet, the sub-Aftonian of Chamberlin, and 



perhaps the Albertan of Dawson. 



2. First interval of deglaciation-, Aftonian of Chamberlin. 



3. Kansan drift sheet of the Iowa geologists. 



iThe Illinois Glacial Lobe, Men. U. S. Geol. Survey, Vol. XXXVIII. , 



^See Cieikie's Great Ice Age, third edition, 1S94, pp. 754-774. See also Jour. Geol., Vol. Ill, pp. 

 270-277, and Vol. IV, pp. 872-876. 



