1844.] 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



11 



THE PHILOSOPHY OF DESERT FORMATIONS. 



( Continued from page i2.) 



In vain, in lliis grand and universal wreck of by-gone existences, 

 will the geologist look for the mixed material composing many of the 

 older soils of Europe: the fossils of the one and of the other speak 

 alike of a common origin, of causes similating to causes, effects to 

 effects; but the mineral kingdom is still in its infancy, is still but par- 

 tially developed: it has naphtha, bitumen, mineral pitch, and bitumi- 

 nous rocks, but no coal: it has the metalloyds in their uncombined, 

 and even in their combined state; but it has neither iron, copper, 

 silver, tin, or other mines of metallic substance ; and, where the me- 

 tals are developed, as M. Guielin truly observes, they are but superfi- 

 cially disposed upon or near the surface of the earth : it has no lacu- 

 strine or terrestrial deposits, no aluminous clays, no formations analo- 

 gous to the lias, no fossils which tell of its previous occupation by 

 terrestrial forms of life; the beds of its lowest valleys and plains, as 

 its most elevated tracks, denote the one common origin, and exhibit 

 properties and fossil bodies common to both. Wherever the fresh 

 waters descend from above, or percolate through the porous strata, 

 there fertility appears ; the soils of the desert, like the island in the 

 midst of the ocean, when favourably disposed, teeming with vegeta- 

 tion, and demonstrating by its abundance and the sterility around it 

 that nature operates by general laws. Every locality has its local 

 phenomena, and from no one portion can we take a sample as illus- 

 trative of the one great whole: the groups and families of mollusca, 

 the chains of reefs, and the beds of marl filled with reliquae, are all 

 peculi.ir to their respective regions, and confined to that geographical 

 area within which alone they can exist. To whatever depth these 

 soils have been explored the same phenomena is presented to obser- 

 vation, and in no one instance throughout these extensive tracks, on 

 digging for water, have vgetable earths or other products generated 

 by their presence been discovered; they are alike deficient of the 

 gems and metals common to older soils, or lands more favourably 

 situate for their development and increase. In these localities dis- 

 posed within rainy regions, or watered by rivers, the mineral kingdom 

 is largely developed, and many of the metals towards the eastern and 

 southern regions of Africa are found in abundance ; but the only metal 

 generally disseminated over the virgin earth is iron in its oxidated 

 state united with calx, or developed in saline beds in the form of 

 iron glance; in this latter state it abounds in Mount Ormus in the 

 Persian Gulf, which elevation is almost wholly composed of muriate 

 of soda: beyond the state of sulphate, phosphate or carbonate, iron 

 ore is rarely or never seen, and only where water is present. Again, 

 in these soils, the stones continue for indefinite periods of time in 

 the petrified state, similating in their general composition and cha- 

 racter; and such is the case with desert sands, the one and the other 

 becoming translucent and crystalline, as they are exposed to the con- 

 joint action of heat and water: thus in the river Nile, many of the 

 sands are exceedingly beautiful, and other of the stones are converted 

 into varieties of quartz and mineral gems. 



All the plains and elevations of the deserti are more or less im- 

 pregnated with salt, and the greater part of the springs are so saline 

 as to render the water wholly unfit for man or animal to drink. By 

 the sea of Abyssinia, the s ilt exists in dry solid masses : the summit 

 of the mountains which border the desert to the west of Grand Cairo 

 present an immense plain, covered with a mass of lalt extending over 

 a surface of 3U or 4U square miles. In the Mesopotamian deserts 

 there is an abundance of rock salt, much of it in very large transparent 

 crystals. In the kingdom of Tunis, mount Had Delfu is entirely com- 

 posed of rock salt, and in lact there are few parts of the desert where 

 it is not to be found. The earths of soda and magnesia are also ex- 

 ceedingly abundant, entering into the composition of rocks, and decom- 

 posed masses of calcareous matter, and giving character to the marls. 



The hills which form the boundaries of Upper Egypt are all of 

 fossil composition, some of them have passed by gradual transition 

 into compact limestone, and when within the reach of the waters have 

 assumed a quartzose structure: others are in the state of soft carbonate 

 of lime, indurating as they become exposed tj the hot dry air, and 

 the fossil shell fish contained therein are discovered in their various 

 stages of conversion into chalk, from which state, on exposure to the 

 atmosphere, they silicify.and eventually become Egyptian jasper. Many 

 extensive formations are wholly composed of Cirrhipedes, pipe corals, 

 ostrae, &c. ; the upper plains exhibit a great variety of species in their 

 fossilized state, particularly echini, ostree, radiati, and other fish of a 

 calcareous nature ; in some places the limpets and rock oysters are seen 

 fossilizing as the ro ;ks indurate ; in fact their changes and re-combi- 

 nations are, generally speaking, indefinite. Many of the hill ranges 

 in the very heart of the Nabian and Suez deserts have a striking 



similarity in character and composition, to the very recent formations 

 bordering the Red Sea, being of a calcareous nature, and containing 

 vast quantities of the same species of marine exuviee : the perpen- 

 dicular fronts of both mark the action of the waters as they have 

 slowly decreased, and their upper surface terminating in considerable 

 plains covered with salt and fossil bodies; and where the dry hot 

 sands have covered in the fossils for a series of ages, they have been 

 preserved from change, so that when taken therefrom, pearl oysters 

 have exhibited all their native freshness, as though recently abstracted 

 from the waters: they also contain aggregates of an indeterminate 

 character between granite and sandstone, or limestone and sandstone, 

 in whii-'h are numerous crystalline secretions of sulphate of iron: 

 some of the beds gradually assuming a lamellated appearance, the 

 fossils and chalk being in alternate layers, as is often exhibited by the 

 chalk formations of this country. In some of the extensive valleys 

 the whole of the fossil bodies spread over the surface are covered 

 with a delicate bloom of sulphate of magnesia; in other places the 

 eye is dazzled by the lustre reflected from crystalline salt or selinite. 



Green marble (serpentine) is very prevalent in the Nubian and 

 Egyptian deserts, rose jasper in its various stages of formation, from 

 the slightly adhesive mass of siliclfying pebbles and calcareous mat- 

 ter, until the whole of the aggregates become united by the silicious 

 waters, jasper is exceedingly abundant, and Mr. Bruce mentions small 

 pieces having green, white, and red spots, called in Italy Diaspo 

 Sanguineo : the granites and porphyries sometimes form entire hills, 

 and with marbles and limestone entire mountains; and the mountains 

 bordering the sea, or those which receive the rains, have a reddish 

 or brownish hue, the calcareous matter spreading over their surface 

 having passed into various stages of change. Both Buchardt and 

 Bruce speak of enormous masses of red granite, hornblende and rose 

 quartz as being exceedingly abundant, particularly near the borders of 

 the Nile, and in the rainy regions. It was from the heart of the desert, 

 between Cosseir and the river Nile that the ancients quarried their 

 fine granites, marbles, and porphvries. 



Of the phenomena of the desert, the moving pillars of sand are not 

 the least remarkable. Bruce says, "we were at once surprised and 

 terrified by a sight, one of the most magnificent in the world. In that 

 vast expanse of desert (Waadi el HabsudJ, from W. to N.W. of us, 

 we saw a number of prodigious pillars of sand at different distances, at 

 times moving with great celerity, at others stalking on with a majestic 

 slowness ; at intervals we thought they were coming in a very few 

 minutes to overwhelm us, and small quantities of sand did actually 

 more than once reach us ; again they would retreat so as to be almost 

 out of sight, their tops reaching to the very clouds. There the tops 

 often separated from the bodies; and these once disjoined, and dis- 

 persed in the air, did not again appear. Sometimes they were broken 

 near the middle, as if struck by a large cannon shot. About noon they 

 began to advance with considerable swiftness upon us, the wind being 

 very strong at north. Eleven of them ranged along side'of us about 

 the distance of three miles. The greatest diameter of the largest 

 appeared to me at that distance as if it would measure 10 feet. They 

 retired from us with a wind at S.E., leaving an impression upon the 

 mind to which I can give no name, though surely one ingredient in it 

 was fear." This phenomenon is common to the deserts of Nubia and 

 Arabia, and generally occurs in plains surrounded by high mountains: 

 it is produced in like manner as waterspouts, by contending currents 

 in the atmosphere, the upper and prevailing current being opposed by 

 the other, changes its force of direction towards the earth, descending 

 in a spiral form, and rebounding from the earth passes upwards within 

 the vortex it creates, until it reaches the prevailing current, when it 

 is immediately broken to pieces; the sands are preserved in their 

 pillar like form by the encircling current. I have often encountered 

 them in the Arabian deserts, with a sensation of pleasure rather than 

 fear, for it does not appear that any danger exists either of being 

 carried up by the whirlwind, or being choked by the falling sands. 



The Samiel (signifying angel of death), sometimes termed the 

 Simoon, is in reality dangerous and deserving its name, and instances 

 of entire caravans having been overwhelmed are related by many his- 

 torians. While in the midst of an extensive plain where all retreat is 

 cut off, it is seen advancing in a dull yellowish fog, extending from 

 the surface of the earth to an inconsiderable height; its outer edge 

 has the copper colour hue of clouds preceding a hurricane in the 

 West Indies ; its searching influence is felt long before it reaches you, 

 and even the camel, shows symptoms of alarm, uttering loud cries; 

 and every traveller falls prostrate with his face towards the earth to 

 prevent suffocation. In one of the Waadis of Nubia I encountered this 

 venomous blast, and as it passed over my prostrate form, every part 

 of my body tingled as though innumerable sparks of fire had come in 

 contact with the flesh. When blown over, which was in about ten 

 minutes, I found my water skins dried up, and the sands on the wind- 



