BY PROFESSOR GRIFFITH TAYLOR, D.SC, B-E., B.A., F.G.S. 195 



this level the temperature \vill be somewhat too cold for the 

 maximum effect, and below this level it will be too w^arm 

 for ice to form. 



We know that there were colder and warmer stages 

 during the Pleistocene Ice Ages. This implies that the niva- 

 tion-layer halted at various elevations in its descent from 

 and ascent to its present elevation of 6,000 feet above sea 

 level. I imagine that we have evidence of two such phases 

 in the topography of the Plateau. At the maximum cold 

 period the layer was at its lowest; and the low-level cirques 

 of Lakes Seal, Hayes, and Belcher were cut out while the 

 great Mount Field glacier moved down the river valley for 

 some five miles as the beautiful moraine crescents (5) clearly 

 show. At this period the edges of the Broad River Valley 

 were "cleaned out" and the cross-section converted from a V 

 into t?ie catenary curve of the glacial type. All the lower 

 moraines were laid down also at this phase. Two well- 

 marked halts are indicated how^ever by the grouping of the 

 moraines, above and below the two enormous erratics in 

 Broad Valley (which I learn from the paper by Mr. Lewis 

 have been named after myself). This stage would be indi- 

 cated in Figure 4 if we imagine the nivation-layer at the 

 lowest level in the section. 



The seven tarns named after Johnston and New^degate 

 lie on a shelf (see Figs. 4 and 5) whose origin can best be 

 explained in a similar fashion, I think. They are at an ele- 

 vation of 4,300 feet, or 1,200 feet above the floors of the 

 cirques described previously. The shelf is about one mile 

 long and varies in width from 80 yards in the south to a 

 quarter of a mile at the somewhat lower -northern end. The 

 whole shelf is jewelled with rocky tarns lying in the hollows 

 betv/een rounded rock hummocks whose surface has certainly 

 been smoothed by ice action. Their most striking feature, 

 however, is the way in which some of the lakelets have two 

 openings, one passing along the shelf to the north, and the 

 other opening directly over the great thausand-feet cliff. 

 Large erratics perch precariously on sloping platforms just 

 as they v/ere dumped by the ice. All this indicates that no 

 long interval has elapsed since the topography was initiated, 

 for the longitudinal drainage of the seven tarns n:ust suffer 

 capture in the near future by the streams flowing directly 

 over the edge. 



(5) These were, I believe, first identified on February 3rd. 1919. 

 See my brief report in American Geographical Review, December, 1919. 



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