Geological Papers. 91 



AN ESKER AT MASON, MICHIGAN. 



By L. C. WoosTER. State Normal School, Emporia. 



I ^URING the summer of 1881, while making a rapid survey of 

 ^-^ the drift deposits of southern Michigan for the United States 

 Geological Survey, I stopped for a day at Mason, about fourteen 

 miles south of Lansing. The surface was then heavily timbered 

 and sloped approximately three feet to the mile towards Lansing., 

 with no elevations of any consequence apart from the esker. This 

 plane topography makes the long, sinuous esker a very conspicuous 

 feature of the topography — one to be reckoned with by the road- 

 maker as well as by the geologist. iMate 1 gives a typical view of 

 a portion of the esker as it exists in 1908, and plate 2 shows its in- 

 ternal structure. Limitations of time forbade my tracing the esker 

 throughout its course, and the nature of the esker at its beginning 

 near Lansing and its southern terminus southeast of Mason are 

 unknown. One tributary was noted from the car window near 

 Mason. The people at Mason say that the length of " the ridge " 

 is about twenty miles, height thirty to fifty feet, and its width, at 

 base, 150 to 400 feet. 



Geologists tell us that eskers mark the course of subglacial 

 rivers, rivers which carried southward the waters of the glacier in 

 its old age. This esker marks the channel of a south-flowing river 

 of the drainage system of the Saginaw glacier, whose terminal 

 moraine (or one of whose terminal moraines) lies a little southeast 

 of Jackson. The present slope of the surface to the northward is 

 due to tlie thicker deposit of drift near the moraine, and not to the 

 slope of the subjacent rock surface. The esker probably loses its 

 identity in the front moraine of the Saginaw glacier, or it may 

 even extend beyond and terminate as a kame or delta on its south- 

 ern slope. 



The component material of the esker is all water-worn, and was 

 evidently deposited through the agency of water. The boulders 

 are of all sizes up to twelve inches. The material of the esker is 

 shown in plate 2, but the boulderets shown in the front of the 

 plate have been through a process of concentration by the removal 

 of the sand for local use. Perhaps forty per cent are sandstone, 

 similar in lithological character to the subjacent rock strata. The 

 remainder are species of metamorphic or igneous rocks similar to 

 those of the neighboring till, with the exception of a red, white 



