132 a Dawis—Gorges and Waterfalls. 
already quoted. We have to thank the old ice-sheet for our 
picturesque gorges as well as for our pleasing lakes. 
It has been suggested that the gorges are in many cases the 
work of subglacial streams during the presence of the ice, 
instead of the effect of open water cutting in later times. Toa 
certain extent this may be true; but when, as so commonly 
happens, there are clear signs of the former existence of a lake 
above the gorge, then the work must be considered essentially 
postglacial. For if the gorge had been cut under the ice 
It is to be hoped that detailed observation may be directed 
to some good examples of these attractive elements of our 
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orms. A set of large diagrams, in which views and mapsof 
Cambridge, Mass,, June, 1884, 
