62 



SCIENCE 



[N. S. Vol. XXX. No. 758 



The Yosemite landscape is characterized by 

 many large expanses of smooth, bare granite. 

 Over these different things move or have moved 

 at various times: water in sheets, rills and 

 streams, snow and glacial ice, and with each of 

 these carriers, rock debris in varying quantities 

 and states of comminution. As a consequence 

 these rook surfaces are scored, marked and striped 

 in sundry ways. The nature of these different 

 markings is well understood; yet there is one kind 

 among them that appears scarcely to have received 

 recognition, namely, that produced by creeping 

 rock debris. It is on gently inclined surfaces, such 

 as obtain on the crowning portions of the Yo- 

 semite domes that the conditions are most favor- 

 able for their development. Loosened rock frag- 

 ments here slide or creep down at the rate of 

 perhaps but a few inches annually. The fric- 

 tional resistance of the smoothly curved granite 

 surface being very slight, but little force is re- 

 quired to propel the fragments in downward direc- 

 tion. IProbably a number of agents are involved, 

 but snow and water no doubt furnish most of the 

 necessary energy. As the fragments advance they 

 leave trails or tracks behind, conspicuous by their 

 whitish color. Close inspection reveals that these 

 consist simply of paths from which the lichens and 

 mosses that cover the rook surface everywhere and 

 give it its subdued grayish tint have been cleared 

 off. So slow is the progress of the debris, however, 

 that the removal of the lichens can obviously not 

 be attributed to mechanical abrasion. Picking up 

 a fragment one finds its base invariably embedded 

 in a pad of loose rock grains. Now lichens can 

 not live under even the thinnest film of sand. 

 The explanation therefore seems to be that the 

 pad of sand grains kills the lichens under it, and 

 as it moves along with the larger fragment, leaves 

 a clean swath behind. The process is evidently 

 as effective on a small scale as on a large one. 

 On the little-frequented slopes of Liberty Cap and 

 the other lesser domes of the upper Yosemite 

 region, where the debris has a chance to travel 

 year after year, undisturbed by man or animals, 

 rocks of every size down to that of a pea were 

 observed, each at the lower end of a whitish track 

 of proportionate width. Some of the tracks were 

 but a few inches long, but many of them measured 

 several yards. On a bared portion of the rock 

 floor of the Little Yosemite Valley the phenom- 

 enon is revealed on a grand scale and wholesale 

 fasliion. Several acres of smooth granite here 

 appear blotched, as it were, with a multitude of 

 long whitish stripes and streaks. The debris by 



which the latter were produced, however, has long 

 since vanished and the rock floor has now a clean- 

 swept look. The cause of the disappearance of 

 the debris may be inferred from the character of 

 the tracks. The latter frequently fork downward, 

 once or several times in repetition. The rock 

 fragments, probably of glacial origin to begin 

 with, must have disintegrated on the way, falling 

 apart in successively smaller pieces, until at last 

 they were resolved into little heaps of loose rock 

 grains that were easily swept away. 



Observations on the Recent Galabrian Earth- 

 quake: Mr. C. W. Weight. 

 This paper was published in the National Oeo- 

 graphio Magazine under the title of " The World's 

 Most Cruel Earthquake," and no abstract is there- 

 fore given here. 



At the 219th meeting of the society, held at the 

 Cosmos Club, on Wednesday evening, April 28, 

 1909, Mr. David White presented an informal 

 communication on " Graphic Methods of Repre- 

 senting the Regional Metamorphism of Coals." 

 He exhibited a map covering a portion of the 

 Appalachian trough on which the fixed carbon of 

 the coals (ash and moisture free) was platted 

 according to the location of analyzed samples and 

 contours were drawn showing the degrees of de- 

 volatilization in passing from the western margin 

 of the coal field to the Anthracite regions. This 

 method not only shows successfully the progressive 

 devolatilization, as the result of deep-seated thrust 

 pressure, of the coal, the greatest alteration mark- 

 ing the greatest pressure, but it also illustrates 

 the fact that folding and faulting, though valid 

 as proof of thrust action, did not always attend 

 the greatest devolatilization, since they, in some 

 instances, undoubtedly gave relief from long con- 

 tinuance of possible maximum pressure, while 

 pressures, perhaps lower but exerted for a longer 

 time, without relief by plication, in contiguous 

 areas, effected greater changes in the fuel. The 

 method was recommended as direct, without re- 

 course to ratios, and simple, being based on proxi- 

 mate analyses. It illustrates in a striking way 

 the improvement of the bituminous coals as the 

 result of regional metamorphism. A similar plat- 

 ting and " contouring " for the same area, of the 

 carbon-oxygen ratios (dry coal, the oxygen com- 

 pensated for sulphur) show these contours not 

 only to conform in general to the fixed carbon 

 contours, but also better to express the regional 

 changes in the " heat value " of the coals. 



