Marshall. — Geological Notes. 563 



sea at Big Bay. The ice that followed this course was of great 

 quantity, and soon eroded the saddle away, and formed the deep 

 basin of Lake Alabaster en its way. As in this low country 

 the ice would be gradually melting away, a " reverse " slope 

 would be formed, and if the terminal face were near the sea 

 in Martin's Bay morainic matter would be deposited there. 

 Finally, when the climate became more genial and the ice melted, 

 the streams that took the place of the glaciers were blocked 

 from Big Bay by the moraine, and flowed down the reverse 

 slope to Lakes Alabaster and Mackerrow, whose waters were 

 then continuous. Since then the detritus carried down by the 

 Hollyford has advanced for and separated Lakes Mackerrow 

 and Alabaster from one another. The course of the upper part 

 of the Pyke, of the Olivine, and Barrier Streams clearly points 

 to Big Bay as the original outlet for their water or their ice. 



The complete filling of the Hollyford Valley with ice also 

 appears to offer an explanation of the formation of the re- 

 markable flat pass between the Olivine and Hidden Falls 

 Streams. This would decrease the grade down the Hidden 

 Falls Valley, for the surfaces of tributary and main ice-streams 

 are always on the same level, consequently the flow of ice was 

 partly dammed back, and some of it flowed over a saddle into 

 the Olivine and eroded it to its present low level. Still fur- 

 ther on some of this ice appears to have passed over gaps from 

 the Oliviue to the Alabaster Valley, where the level of the ice- 

 surface, owing to the small amount of gathering- ground in that 

 locality, and its proximity to the glacier-snout, was less. 



One important fact in regard to the physiography of this 

 region is the very different levels of streams on opposite sides 

 of mountain-ridges. For instance, the Rock Burn floor is 

 1,000 ft. higher than that of the Hidden Falls Stream, on the 

 other side of the pass. The Olivine floor is 3,500 ft. above 

 Lake Alabaster, though only separated from it by a narrow 

 rock ridge. Instances might be multiplied indefinitely. They 

 seem to point to the probability that here some cause has com- 

 pletely upset the usual drainage conditions of areas of high 

 land. Since this disturbing agent has ceased to act the normal 

 relations of drainage valleys and systems have not been esta- 

 blished, because sufficient time has not yet elapsed. 



That ice is capable of just this disturbance that is here 

 found I believe to have been fully established by geologists. 

 To my mind no writer has more fully stated the peculiarities 

 of glacial valleys than Professor A. Penck, of Vienna, and Pro- 

 fessor W. M. Davis, of Harvard. More especially has this been 

 done lately in the " Journal of Geology," where Professor 

 Penck, writing on the " Glacial Features on the Surface of the 



