196 



SCIENCE. 



[Vol. V., No. 109. 



taken his parting glimpse of his palace of the 

 Alhambra, the rich Vega, and ' Grenada the 

 marvellous.' It is appropriately named ' Sus- 

 piro del Moro ' (' the Moor's sigh'). 



A very few men can safety hold the entrances 

 to the Alpuj arras ; and they long remained the 

 last stronghold of the Arab power in Spain, 

 which has passed, leaving as its memorial lit- 

 tle more than the names of a few villages, and 

 the wonderful system of irrigating- works. 



There can hardly be a doubt that the series 

 of calamities, hardly closed, which has laid so 

 many villages in ruins since last Christmas, is 

 a continuation of the processes \>y which por- 

 tions of the earth's crust are raised in moun- 

 tain ranges above the rest. A few words on 

 the geological structure of the sierra may in- 

 dicate the possibilities of the localit} T . The 

 structure of the sierra and its neighbors is 

 quite simple. The}' rise like islands or domes 

 of ancient mica schists out of a sea of later 

 formations, which break like waves upon their 

 flanks. These schists are of a silvery white, 

 appearing like snow when distant and illumi- 

 nated by the sun. They are absolutely sterile, 

 but dip, in a general way, outward from the 

 central axis of elevation in all directions. A 

 belt of radiatety dipping Silurian schists encir- 

 cles the central part of the sierra, which, like 

 the exposed part of the core, assumes rounded 

 outlines, but is succeeded b} r another belt, rug- 

 ged, precipitous, and cragg} T , of Permian lime- 

 stones, which extends to the base on the 

 eastward, but is nearly as irregular in height 

 as in extent. The Alpujarra basins are ex- 

 cavated in these limestones, and protected by 

 escarped cliffs. Against the base of the sierra, 

 raised slightly near the mountains, but else- 

 where horizontal, lie tertiary grits, clayey sands 

 and clays, deposits of fine gypsum, etc., cov- 

 ered with two alluvial series of beds, — the 

 lower composed of decomposition products of 

 the Silurian schists, brought down by water 

 and mingled with material derived from the 

 subjacent tertiaiy ; the upper and later, from 

 the denudation of the fundamental mica schists 

 now forming the crests of the sierras. Moule 

 observes that the elevation of the sierras has, 

 in part at least, taken place since the tertiary 

 epoch, and even since the alluvial period, and 

 that it may not yet have ceased. This obser- 

 vation, written before the recent disturbances, 

 has found in them renewed support. 



The people of the country, finding in the 

 elevated blocks of argillaceous alluvium left 

 isolated b}^ the torrential rains of part of the 

 year a soft but compact and resisting mate- 

 rial, have carved in them whole villages of 



cave-houses, with doors and windows, and 

 often with one story above another. These 

 abrupt elevations, though of moderate height, 

 are extremely numerous, entirely without vege- 

 tation, and of »an ashy hue. The cave vil- 

 lages are numerous, and, as in the case of 

 Purullana, contain sometimes several hundred 

 inhabitants. One ma}- imagine the devasta- 

 tion among these gnomes which an earth- 

 quake shock must produce, and which would 

 go far to explain the great loss of life in these 

 small places. 



The shocks felt have been chiefly to the 

 westward of the Sierra Nevada, and have been 

 most severe along the junction of the tertiary 

 rocks with the schists. Here towns have been 

 almost or quite destro} T ed, and the ruin 

 wrought has been largely proportional to the 

 proximity of the town or village to the uncon- 

 formability of the rocks, though the motion 

 has been propagated over a much wider 

 area. 



THE WORK OF THE SWISS EARTH- 

 QUAKE COMMISSION. 



The Swiss earthquake commission was appointed 

 by the Swiss society of natural sciences, in 1879, to 

 secure more uniform and accurate observation and 

 study of the seismic disturbances in and around the 

 Alps. It included such men as Forel, Forster, Ha- 

 genbach-Bischof, Heim, Soret, and others of mark 

 as physical-geographers and geologists ; and they at 

 once began an active campaign. Professor Heim of 

 Zurich wrote several general articles l to call atten- 

 tion to the undertaking, and to outline the method 

 by which intelligent persons could give effective 

 assistance ; and since then, he and Forel, both admi- 

 rably qualified, have prepared a number of mono- 

 graphic reports on the results thus far reached. The 

 official journal of publication is the Jahrbuch des tel- 

 lurisches observatorium of Bern; but, so far as I can 

 learn, none of our libraries possess a copy of it. 

 Fortunately, the reports have mostly been reprinted 

 in periodicals of more general circulation, and from 

 these the notes here presented are derived. 



Forel' s entertaining papers 2 give the results of the 



1 Ueber die untersucbungen der erdbeben und die bisherige 

 resultate. Zurich vierteijahresschr., 1879. 



Die erdbeben und deren beobacbtung. Zurich, 1880. This 

 appeared also in French, translated by Forel, in the Arch, des 

 sciences, iii. 1880, 261. 



Die schweizerischen erdbeben von November 1879 bis ende 

 1880. Jahrb. tellur. observ., 1881; with an appendix giving im- 

 portant corrections. 



2 Les tremblements de terre etudies par la commission sismo- 

 logique suisse de novembre 1879 a fin de 1880. Arch, des sci- 

 ences, vi. 1881, 461. 



Id. . . . pendant l'annee 1881. Arch, des sc, xi. 1884, 147. 

 Les tremblements de terre orogeniques etudies en Suisse. 

 UAstronomie, ii. 1883, 449; iii. 1984, 13. 



