Page:Science vol. 5.djvu/214

 taken \m parting glimpse of liis palace of the Albambra, llie rich Vega, and ■ Grenada the marvellons.* It is appropriately named ' Sus- piro del Moro ' (' the Moor's §igh').

A very few men can safely liold the entrances to the Alpnjfliraa ; 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 hiirdly be u 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 by which por- tions of the eni'th'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 locality. The structure of the sierra and its neighbors is quite simple. They rise like islands or domes of ancient miiia schists out of n 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- ii^«d by the sun. They are absolut«lj' sterile, but dip, in a general way, outward from the central axis of elevation in all directions. A belt of radiately 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 by another belt, rug- ged, precipitous, and cra^y, 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 Ctora the subjacent tertiary; the upper and later, from the denudation of the fundamental mica schists now forming the crests of the sierras. Aloule 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 maj- 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 ai'gillaceous alluvium left isolated bj' the torrential rains of part of the year a soft but compact and resisting mate- rial, have can-ed 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 extremelj' numerous, entirely without vcge- tation, and of an ashy hue. The cave vit l&ges arc numerous, and, as in the case ml' Purullana, contain sometimes several hundred inhahitanta. One may 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 thess small places.

The shocks felt have been chiefly to westward of the Sierra Nevada, and have beea most severe along the junction of the terljaiy rocks with the schists. Here towns have beeR almost or quite destroyed, and the ruin wrought has been largely proportional to thft proximity of the town or village to the uncoM' ibrmability of the rocks, though the motion has been propagated over a much widKt-

��THE WORK OF THE SWISS EARTH- QUAKE COMMISSION.

The Swiss earthquake commiMlon wm appoloWd by the Swiss society o[ natural sciences, in 1879, to secure more uniform and accurate ob^ervatioD and study of the seismic disturbances [ii aud around Iht Alps. It included such men as Forel. Forster, Ha- geubacb-BIschor, Heim, Soret, and others o( mark as physical-geographers and geologisu ; and Ihej U <mce began an active campaign. Professor Helm of Zurich wrote several general articles' to call atten- tion to the niiderulting, and to outline the method by which Intelligent persons could give effective aasistance: and since tlicn, he and Forel, both admi- rably qualified, have prepared a number of graphic reports on the results thus far reached. official journal of publication is the Jaht^uch de» lurfscAcB obfeTvatorium of Bern; but, so far ai learn, none of our librariea poaae»8 a copy Fortunately, llie reports have moati; been reprini in periodicals of more general circulation, and fi these the notes iiere presented are clerlved.

Forel's entertaiuing papers ' give Lbe resulu of

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