210 PLEISTOCENE OF INDIANA AND MICHIGAN. 



a uniform course approximately S. 20° E., then changes abruptly to about S. 70° E., and so 

 continues for 2 miles or more, when it reunites with the valley of Sycamore Creek. For 3 miles 

 the united valley takes a course fluctuating between S. 20° E. and S. 30° E.; then it changes 

 and runs S. 50°-70° E. to the Mud Creek valley at the inner border of the Charlotte system 

 where it swings abruptly south and follows the creek to its source in the northeast part of Leslie 

 Township (T° 1 N., R. 1 W.). Its form changes with its trend, being deepest where it runs 

 S. 20° E. and shallowest where it passes eastward to join the Sycamore Creek valley; it deepens 

 again when combined with the Sycamore Creek valley but shallows in crossing over to Mud 



Creek. 



Topography. — In the first 3 miles of its course the esker consists of short ridges interrupted 

 by longer gaps, one of which, 2 miles south of Cemetery Hill, gives passage to Sycamore 

 Creek. Farther south, beyond the point where the esker trough reunites with the Sycamore 

 Valley, the esker makes several abrupt turns but keeps within the limits of the valley. 

 (See PI. VIII.) Its interruptions are slight, apparently aggregating scarcely one-sixth of 

 the combined length of the constituent ridges. The height of the ridges varies consid- 

 erably and in places changes abruptly, dropping off in a few yards from 40 feet to less than 

 10 feet and even terminating abruptly to reappear within a few rods as a low ridge. On account 

 of these abrupt breaks it has been used as a wagon road for but a short distance. Its width 

 is only 50 to 100 yards even when highest, and its slopes are very steep, reaching 30° in places. 

 The ridge is especially prominent where it makes the eastward deflection to come back to Syca- 

 more Creek near Mason, its height being 20 to 30 feet above the bordering till plains. The 

 esker passes directly through the city of Mason, where, for a short distance, it lies well up on 

 the east slope of the valley, and rises above the bordering upland. For about 2 miles south 

 of Mason it is 30 to 40 feet in height and practically continuous. After leaving Sycamore Creek 

 in sees. 21 and 22, T. 2 N., R. 1 W., it is low and interrupted by gaps for a mile or more, but on 

 the swampy divide between Sycamore and Mud creeks it is broken by only narrow gaps. In 

 the vicinity of the Charlotte morainic system it expands into a series of kames or plexus of 

 ridges which inclose swampy depressions. Around the southern end of this kame plexus the 

 moraine itself is exceptionally gravelly over an area of about 10 square miles, a feature which 

 is perhaps due in part to the same subglacial drainage that produced the esker. 



The course of the subglacial stream which formed the esker, as is shown by the bedding of 

 the gravel, was from north to south, or the reverse of the present drainage, and the elevation 

 of the esker trough increases in passing from the head southward, being about 830 feet near 

 Lansing, 900 feet at Mason, 11 miles up Sycamore Creek, and about 915 feet at the southern 

 terminus 7 or 8 miles farther south. It therefore ascends about 85 feet in less than 20 miles. 

 If the gravelly portion of the moraine adjacent to the southern end of the esker trough be included 

 the rise is 50 to 75 feet more, to the summits of the most prominent knolls. This rise is made 

 abruptly, in places in less than one-half mile. It is doubtful if the stream which formed the 

 esker and esker trough really made such an ascent. The esker trough seems likely to be a result 

 of depletion of the basal portion of the ice by streams within the ice rather than beneath it. If 

 so, the streams may have made little or no ascent. 



Composition. — The esker, wherever opened, is composed of stratified and more or less 

 perfectly assorted material. It gives evidence of the action of a stream which varied greatly 

 in the rapidity of flow in different places along a given horizon, both longitudinally and from 

 side to side, as well as at different horizons. The phenomena displayed are not unlike those 

 found in the beds of existing streams flowing subaerially. The esker is evidently a stream-bed 

 deposit, though probably deposited within ice walls. 



The most extensive excavation is a railway gravel pit about a mile south of Mason. The 

 esker here has a height of 35 to 40 feet and a breadth of only 50 to 75 yards at the base. The exca- 

 vation is about one-fourth mile in length and passes obliquely through the esker, its southern end 

 showing the structure of the east side and its northern of the west side, the main part of the 

 exposure being in the elevated central portion. The eastern slope is underlain by fine sand 

 but the main body of the ridge is of gravel. It has a capping of brown clayey gravel, varying 



