February 4, 1892] 



NATURE 



319 



frequently cut completely through the nevi zx\A expose the rock 

 beneath to the action of frost. In such instances the rocks are 

 in the best position possible to be acted upon by great changes 

 of temperature. Dark bodies on high mountains absorb heat 

 when exposed to the sun, although the air may be below 32° F.; 

 and melting the adjacent snow, become saturated with water, 

 which freezes as soon as they are in shadow. The blocks thus 

 loosened fall away or are removed by the motion of the neve. 

 The tops of the cliffs, however, are protected by a covering of 

 snow. There is frequently a space above the top of the nhji in 

 summer which is exposed in like manner to the aclion of the 

 atmosphere. These slopes recede by sapping through the action 

 of frost, and precipices result. While the upper portions of the 

 walls of depressions filled with nt'vesi\ovi are being broken away 

 by the tensions in the neve, and by atmospheric action, the 

 snow on the lower slopes is under compression, and thus 

 rendered capable of abrading the rocks over which it flows. 



The ice, in descending the steep slopes from various sides, 

 impinges with great force on the bottoms of the depressions it 

 occupies, and tends to scoop out rock basins. The result of 

 these combined agencies is seen when the nM'is removed, and 

 we find amphitheatres with precipitous walls rising immediately 

 above a rock basin lake. In other words, the resulting form is 

 a cu-que like those of the High Sierra. 



So far as my observations extend, cirques are confined to 

 mountains on which ice sculpture followed water sculpture. 

 The topographic forms left after the disappearance of the ice 

 are modifications of the antecedent forms due to the action of 

 lain and streams. 



In the vicinity of Mount St. Elias, Alaska, the mountain 

 ranges are primarily monoclinal uplifts of geologically recent 

 date, and do not bear evidence of having been deeply dissected 

 by streams previous to the birth of the present glaciers. The 

 ice drainage is largely consequent on the present orographic 

 structure, and cirques are usually absent. One remarkable ex- 

 ception to this is furnished, however, by a fine cirque on the 

 southern side of St. Elias, which is filled by neve snows and 

 drained by a small glacier. Thousands of secondary and ter- 

 tiary glaciers exist on the southern slopes of the mountains, but 

 certainly very few, and so far as my knowledge goes none, of 

 these have their origin in true cirques. On the north side of the 

 mountaics, however, which are in general the gently sloping 

 surfacesoforog'iiphic blocks, topographic forms inherited from 

 former aqueous erosion are conspicuous, and cirques are 

 abundant. 



Glaciers exist about the summit of Mount Shasta, Mount 

 Ranier, Mount Baker, and other high volcanic peaks in the 

 Cascade Mountains, but none of these, so far as known, originate 

 in cirques. These mountains, like the uplifts about Mount St. 

 Elias, are geologically young. They are volcanoes with fuma- 

 roles in their craters ; and owing to their elevation, and the com- 

 paratively slight erosion they have suffered, it is reasonable to 

 suppose that the first precipitation on their summits was in the 

 form of snow. Glaciers were formed on unmodified slopes, but 

 have not excavated cirques for themselves. The glaciers on these 

 mountains, like many of the smaller ice streams in Alaska, 

 occur on exposed slopes and not in depressions. The accumula- 

 tions of snow and ice form prominent convex surfaces and fre- 

 quently give a characteristic outline to the summits which they 

 cover. 



The probable origin of cirques which I have traced, together 

 with the fact that they occur in thousands about the summits of 

 mountains on which the glaciers followed water sculpture, 

 together with their absence on unglaciated mountains like the 

 Southern Appalachians, and also the fact that glaciers in them- 

 selves do not seem to have the power of excavating similar 

 depressions, is seemingly cumulative evidence pointing to the 

 conclusion stated above. 



Cirques, alcoves, and possibly other forms, when considered 

 simply as topographic features, may perhaps be classed together ; 

 yet, genetically, alcoves and cirques are distinct, the former 

 owing their existence to aqueous sculpture, usually in horizontal 

 rocks, and the latter to aqueous sculpture followed by ice sculp- 

 ture, in rocks which may be heterogeneous or homogeneous, 

 horizontal or inclined. 



The generalization that ^* cirques are confined to glaciated 

 regions," to which Mr. Bonney takes exception, was reached 

 from considering the distribution of typical examples, previous 

 to the differentiation of cirques from other similar topographic 

 forms. When they are recognized as distinct from alcoves, and 



necessarily in part of glacial origin, the reason for their distribu- 

 tion becomes evident, as does also the further generalization 

 that they "occupy localities where glaciers first appear." 



In the Rocky Mountains the peaks and ridges on which 

 cirques occur have an elevation of from 10,000 to 14,000 feet. 

 The same is true also in the Sierra Nevada. In each of these 

 regions the ancient nevi fields had generally about the same 

 elevation, while the glaciers flowing from them descend to 

 within 6000 or 5000 feet above sea-level. In Alaska, however, 

 where the former glaciers descended into the ocean, cirques 

 occur on peaks and ridges only 3000 or 4000 feet high, and 

 exaniples may be found at elevations of less than 2000 feet. 

 Their vertical, as well as their geographic range, therefore, 

 appears to have been regulated by the climatic conditions which 

 control the birth of local glaciers. 



While "alcove "and '^'^ cirque" should have a definite sig 

 nificance in geology, amphitheatre, recess, bowl, and other 

 correlative woi ds, may be considered as general terms applicable 

 to more or less inclosed spaces without reference to their origin. 

 TJie semicircular recesses made by winding stre.ams in the 

 sides of canons and deep valleys, sometimes resemble alcoves. 

 Craters frequently bear a close topographic similarity to cirques, 

 but are readily distinguished when their origin is considered. 



On looking over my account of the cirques of the High 

 Sierra (Eighth Annual Report, 1886-87, U.S. Geological 

 Survey), I fail to discern any reason for materially changing 

 it, except, as indicated above, to state more definitely the differ- 

 ences between cirques and other topographic forms with which 

 they might be confounded. 



I remain very sincerely your friend, 



Israel C. Russell. 



Large Meteor of January 24, 1892. 



It is to be hoped that further observations will be forth- 

 coming of the brilliant meteor of January 24, loh. 55m. (de- 

 scribed by Mr. T. Heath in your last number, p. 295), so that 

 its real path may be computed. I think there is little doubt 

 the meteor belonged to a shower of Draconids having a radiant- 

 point a few degrees south-east of the star C- On the same nighi 

 (January 24) as that on which the fine meteor was observed, I 

 saw a third magnitude shooting-star, at 7h. 5Sm., with a path 

 from 324° -t- 40° to 330^° -f- 31^°, and this also belonged to the 

 radiant in Draco. I discovered this shower on the nights of 

 January 19 and 25, 1887, and determined the position of the 

 radiant as at 261° 4- 63°. There are many other showers from 

 the same point in the spring, summer, and autumn months. 



Bristol, January 31. W. F. Denning. 



On the Relation of Natural Science to Art. 



In Dr. du Bois-Reymond's interesting lecture, as published 

 recently in Nature, there occurs the following passage (p. 226) : 

 "Flaxman" was "certainly mistaken in representing Poly- 

 phemus with three eyes — two normal ones which are blind, 

 and a third in the forehead." Does not the recent discovery of 

 a third (parietal) eye in some of the lizard and fish tribes (not to 

 mention the tunicales !) diminish the force of this assertion ? 

 Flaxman's genius appears rather to have forestalled the dis- 

 coveries of science in representing the human monster with three 

 eyes, especially as Wiedersheini states that even in man nerve- 

 fibres have been traced from the optic thalami to the pineal 

 gland. W. AiNSLiE HoLLis. 



Brighton, January 11. 



Ice Crystals. 



The following account of some very well defined ice crystals 

 may be of interest. 



On December 26, 1891, the thaw set in. On the 27th, I 

 noticed on the surface of the ice on the lake at Drinkwater 

 Park, near Prestwich, on the outskirts of Manchester, a large 

 number of very distinct, hexagonal, tabular crystals. The 

 surface of the ice was not very wet. These crystals varied from 

 half an inch to three inches across, were raised about an eighth 

 of an inch above the surface of the ice, and in many cases bore 

 a similar but much smaller crystal in the middle, raised about 

 an eighth of an inch above the surface of the larger crystal. 

 In some specimens the smaller crystal was rounded and indis- 



NO. II 62, VOL. 45] 



