Rev. 0. Fisher — On Cirques and Taluses. 11 



now testified to by the moraines described by Mr. Bonney as being 

 left within their areas. The question, whether the existence of a 

 glacier within the area was or was not necessary to the removal 

 of the talus, may be almost decided by observing whether the talus 

 is or is not at present accumulating. For my own part I have a 

 difficulty in conceiving the removal of talus from an area of such a 

 form by streams. And Mr. Bonney when telling of the accumulating 

 talus, says, "In not a few corries and cirques the transporting power 

 (of streams) can hardly keep pace with the excavatory." " Hardly " 

 is a word of doubtful signification. I have an idea that " not " 

 would express the fact better, for he has just told us how in this 

 one " the ice-worn slopes below are strewn with debris, and " how 

 " their junction with the cliff is almost everywhere masked by 

 screes." If the talus grows, the inevitable result must be that the 

 vertical face will become in time a slope. The slope once completed, 

 the excavation of the true cirque-wall must cease. 



Thus I conclude that a cirque, though not excavated by a glacier, 

 is strictly a glacial phenomenon. 



The mountain tarns, so common in cirque-like hollows, are easily 

 accounted for on the above principles. The tarn occupies the former 

 bed of the glacier, and the dam, which holds back the water, is in 

 the position held by the terminal moraine at the time when the 

 glacier finally disappeared. I can see no other possible explanation 

 of this common feature in mountain scenery. 



But when we come to seek an explanation of the shape of the 

 cirque, the case is not so clear. If they were always in places 

 where many streams from above converge, this might, as Mr. 

 Bonney suggests, cause a more rapid destruction of the rock at that 

 locality; chiefly, however, I should suspect, by atmospheric action 

 on the wet surface. A quaquaversal dip would^soJ)e favourable to 

 the production of a cirque ; the reason being, fe&a&s© the maximum 

 resistance to destruction is not attained until the exposed face is 

 perpendicular to the plane in which the dip lies, or, in other words, 

 is parallel to the strike. The exposed lines of bedding would in 

 that case appear horizontal. 



In a homogeneous rock a hollow once formed would become 

 enlarged by disintegration in all directions equally, so that a vertical 

 chasm would in time become a cirque. Such may be the principle 

 on which cirques in Syenitic rocks may have been formed. 



There is much significance in general about a talus. One of the 

 most remarkable features in mountain scenery is the range of talus 

 which usually borders the valleys, and which is so often clothed 

 with forest. These taluses are unmistakably the last formed feature 

 of the landscape. They belong pre-eminently to the present period 

 of geological change. Previously to their formation the valleys 

 must have had precipitous sides, constantly dropping stones and 

 earth, which must somehow have been continuously carried away. 

 "What carried them away ? The answer must be, either sea or 

 glacier. Few, I suppose, will refuse to give the preference to the 

 glacier. Geologists may differ as to the extent to which these great 



