8 10 THE JOURNAL OF GEOLOGY. 



ing power by increasing their slopes. The front lobes are too 

 strongly shown in the photograph, Fig. 2, as they were left to 

 show the limits of the delta. In the papier-mache' copies, the 

 water completely covers the slopes of the lobes. 



On this deposit, which is 4000 feet from east to west, and 

 2000 to 3000 feet from north to south, there is only one small ket- 

 tle-hole. This lack of kettle-holes, so abundant elsewhere, may 

 be taken as an indication that the ice-sheet was comparatively 

 continuous at this time. It evidently became more broken 

 immediately after the course of the esker stream was changed, 

 as there are several kettle-holes to the north of the sand-plain. 



8. Snperglacial streams. — These are represented on the model 

 as smaller than the main channels below, and more inconstant in 

 direction. Their development after the closing up of the cre- 

 vasses has been made the subject of special study, and its results 

 are shown on the model. Other conceptions of this surface will 

 no doubt occur to many, and any criticism or suggestion will be 

 gladly received. One of the processes that has been a promi- 

 nent factor in the determination of the form of the surface is 

 that described above, where the detritus in the bed of the stream 

 protects the underlying ice. Little accidents of melting and 

 washing would shift the course of these streams, so that the 

 arrangement of them upon the surface would not be shown by 

 any deposits to-day. As soon as one of these streams found an 

 opening through the ice, a moulin would be formed. 



9. Moulins and kames. — In the second model I have made 

 moulins in the ice-sheet above the kames in the first model, 

 though I should not like to be understood as affirming that all 

 these kames were surely formed in this way. It is quite proba- 

 ble that further study would show facts pointing to several gen- 

 eses. Professor Chamberlin says, in speaking of the formation 

 of similar deposits : 



" No existing agency, by any extension of its magnitude, is at all compe- 

 tent to account for their localization. The formative agency, or combination 

 of agencies, must have produced, at once, local assortment and local heaping 

 of the assorted material, or, in other words, the assorting waters must have 



