G. F. Wright — Unity of the Glacial Epoch. 353 



That Professor Chamberlin has kept his mind open to 

 further light is abundantly evident by comparing his account 

 of " the terminal moraine of the second glacial epoch," in this 

 preliminary paper, with that which appears in his later publi- 

 cations, while at the same time such a comparison is suggestive 

 of possible mistake in his whole interpretation of the facts 

 bearing on the duality of the epoch. In this preliminary 

 monograph (see pp. 322-326) the moraine is made to corre- 

 spond with the kettle moraine of Wisconsin, and to hug 

 the southern shore of Lake Michigan, but in the Seventh 

 Annual Report of the U. S. G. Survey the later glacial drift is 

 carried down to Bloomington more than a hundred miles 

 farther south, while at the latest date Mr. Leverett (Am. Geol. 

 July, 1892, p. 23) specially deputed by Professor Chamberlin 

 to look after the moraines, draws his later moraine line one 

 hundred miles still farther south, through Litchfield, Hillsboro, 

 Pana, Shelbyville, Mattoon, Charlestown, Paris and Terre 

 Haute. From other information I have evidence that proba- 

 bly this moraine will have to be carried, at least, twenty-five 

 miles still farther south to Greenville, which will be less than 

 80 miles from the extreme limit of glaciation as determined 

 by me. From this it seems not unlikely that in the near 

 future the closer observation which has found an exterior 

 moraine 200 miles farther south than was at first supposed to 

 mark the limit of the second age, may carry it fifty or sixty 

 miles farther south still, which would be all that it is necessary 

 to make the extreme boundary stand related to the moraine 

 there as it does throughout the eastern part of the Mississippi 

 Yalley. This result is the more likely to occur since for a 

 hundred miles or more the whole border of the glaciated area 

 in the valley of the Mississippi is so deeply covered with 

 loess that the determination of moraine deposits is peculiarly 

 difficult. Mr. Leverett has already found twelve receding 

 moraines in Ohio — the outer one extending to within a few 

 miles of the glacial boundary. When as many are found in 

 Illinois it will, at the existing rate of separation, carry the line 

 as near the border in that State. 



The facts pointing toward a separation of the glacial period 

 into two distinct epochs are thus stated by Professor Cham- 

 berlin in his monograph on the Driftless Area (pp. 214, 215). 

 " The earlier drift is characterized in the interior basin, [1.] by 

 a wide but relatively uniform distribution, manifesting only 

 occasional and feeble tendencies to aggregation in morainic 

 ridges. [2.] It is not bordered, except in rare instances, by a 

 definite terminal moraine, but ends in an attenuated border. 

 [3.] It is not characterized by the prevalence of prominent 

 drumlins or other similar ridged aggregations. [4.] The phe- 



