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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-maché 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 kettle-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. Superglacial 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 crevasses 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 prominent 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 probable that further study would show facts pointing to several geneses. Professor Chamberlin says, in speaking of the formation of similar deposits:

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