THE ONYX MARBLES. 573 



plateaux. The agave, the lefresliiug i)lumpaess of whose virgiu leaves 

 stands out in marked contrast with the dried and shrunkeu forms of 

 the flower-bearing adults, forms, together with the thorny Fouquieria 

 splendens, the most striking floral feature of the waterless land. The 

 onyx occurs in the form of spasmodic and isolated ])atches, sometimes 

 forming apparently a superficial pavement upon the surface, or again, 

 where the beds have been cut by the winding course of the now dry 

 ravine in the form of three distinct layers, from 20 inches to 3 or more 

 feet in thickness, interstratified with tufaceous and lake bed material. 

 (PI. 10). 



Nothing can be more fascinating to the lover "of the beautiful in 

 stoues than tliis occurrence, where huge blocks of material of almost 

 ideal soundness, with ever varying shades of color and veination lie 

 everywhere ex])osed in countless numbers. Under the blistering sun 

 of an almost tropic climate the exposed blocks have become to some 

 extent corroded, and covered upon their immediate surface with a thin 

 film of oxidation products which just sufficiently disguise the true 

 color and transluceucy to keep one running here and there, ever 

 cracking off new fragments in the vain attempt to collect a fairly 

 typical series. The colors are peculiarly delicate, and there is a 

 wonderful uniformity in quality. Pearl white ( the virgin onyx), deli- 

 cate rose tints, and light greens are the more co mmon, all variegated 

 by a network of fine sharj) veins of a rose-red co lor, as shown in Plates 

 17 and 18 The rose color is, so far as my present knowledge goes, 

 quite unique and wonderfully beautiful. 



The analyses given in the table show this to be the most dense of any 

 of the onyx marbles thus far examined. Although less highly colored 

 than some of the Mexican varieties, it is nevertheless one of the most 

 beautiful, owing to its uniform translucency, freedom from flaws, and 

 fine veination. 



Algeria. — The celebrated dejjosits from whence the ancient Romans 

 drew their supplies of onyx, alabaster, calcareous onyx, or oriental 

 alabaster are situated in the northern part of Algeria, in the province 

 of Oran. The deposits as now worked are two in number, one some 05 

 miles from Oran, on the route to Tlemcen, and the second a few miles 

 to the west, both lying to the right of the Isser. The first of these, 

 known by the name of Bled Bekham, is divided into three parts by 

 two ravines, the Oiied Abdallah on the east and the Oued Calkra on 

 the west. M. Comynet estimates the area occupied here by the onyx 

 as about 12 acres, and gives the following section: (1) A bed of 

 about 4 feet thickness, under which lies compact travertine of no value j 

 (2) a second bed of onyx 3 feet 4 inches thick, separated by impure 

 travertine from a third bed of onyx 2 feet in thickness, and lastly, 

 several thinner beds from to 16 inches in thickness, alternating 

 with impure travertine, making in all a mean thickness of some 10 

 feet of quarryable material. It was stated at the time that blocks of 

 extraordinary size could be quarried for shafts, columns, or friezes, 



