No. 104.] . 219 



ties; and even in these it maybe well to inquire whether other causes 

 have not combined with this one, to produce the results recorded.* 



I have received from Prof. J. P. Lesley, of Philadelphia, the following 

 observations regarding the influence of climate in different localities, 

 upon stone of identical or similar character. In speaking of the dura- 

 bility of stone in ancient structures it becomes necessary to know the 

 conditions of climate before a just comparison can be made. 



" One of the two obelisks erected by Thothmes III, at Heliopolis 

 fifteen or sixteen centuries before Christ, was transferred to Alexandria *. 

 and is now known as Cleopatra's Needle. It is of sienite, so streaked 

 with hornblende, obliquely, as to suggest original stratification. 

 Along these streaks, which are of irregular width, atmospheric erosion 

 haa taken place, by the ejection of one group of crystals after another, 

 upon the melting away of the felspathic element. The whole face 

 of the stone has suffered from the same action, but generally to a less 

 degree, than at these exceptional places. Especially all tlie sharp cut 

 edges have been rounded off. Wherever the solar disc, for instance, 

 occurs, there is now nothing but an unsightly hollow, where originally 

 had been cut a sharp clear circle, with a vertical wall around a central 

 convex tympanum. 



thus: 



now: 



" All the hieroglyphs from pyramidion to base have suffered in this 

 "Way. Some are almost indistinguishable, except in the very best slant- 

 ing light of the sun. One or two of the four faces also have suffered 

 more than the others, showing that the prevailing winds have deter- 

 mined the degree of erosion. The climates of Cairo and Alexandria 

 are so different from one another, the former so constantly dry and 

 the other so uninterruptedly wet, that we have a right to ascribe the 

 most of this destruction to the sea air since the removal of the obelisk 

 from its original to its present site. But all the monuments of Egypt, 

 at least up to the first cataract, show marks of atmospheric erosion, 

 in spite of the loose assertion often repeated by travelers, that they are 

 as fresh and their lines as sharp as when the chisel cut them. This 

 is not true of any monument in the open, air ; but is approximately 

 true oE the intaglios in the tombs. Many of the monuments of the 

 middle and classic empires are built of such inferior kind of stone, the 

 only wonder is that they have not tumbled into ruin themselves, 

 through the slow wear and tear of the surface, by the atmosphere. 

 And yet Egypt is one of the driest parts of the world. It must be re- 

 membered, however, that the stratum of air, which lies at night upon the 

 broad bottom of the valley, is charged with the exhalations of the 

 liver, canals and irrigated fields, and in this stratum the monuments 

 stand. When the sun rises this moist air-mass is broken up and car- 

 ried over the mountain walls into the desert." 



* It may perhaps be worth while to inquire whether the effects ascribed to sulphurous 

 gases are really due to .such influences alone. A writer in the "Builder," for Oct. 30, 

 1858, says that the river front, "to the height of the area windows, was built of the Bolso- 

 ver moor stone, but that the remaining upper part, to my wonderment, was built of stone 

 obtained from Anston, in Yorkshire, a t^tone not even alluded to in the report," i. e., the 

 Eeport of the Commissioners. If tliis be true, the theory adopted in explanation of the 

 cause of decay may require some modification. 



