388 DONALD C. BARTON 



fresh and show merely an infinitesimally thin film of tarnish and 

 alteration. Tapping revealed no incipient exfoliation. In micro- 

 scopic thin sections taken at right angles to the surface of a block, 

 the orthoclase is seen to be comparatively fresh; the oligoclase is 

 much clouded by decomposition products, but the alteration is not 

 sufficient to obscure the specific determination of the feldspar. 

 The ferro-magnesian minerals show slight decomposition and in 

 one of the sections there is considerable limonitic staining. The 

 degree of decomposition is no greater than that which is very 

 commonly observed in sections of granite and is no greater toward 

 the surface than deeper in. There is no tendency, as far as could 

 be seen, toward incipient rifting parallel to the surface. The 

 sections were taken at right angles to surfaces which had a southerly 

 exposure and which were therefore exposed to the maximum heating 

 effects of the insolation. 



Farther north in Egypt the rate of disintegration is more rapid. 

 At Luxor, Thebes, Gizeh, and in the museum at Cairo, the granite 

 (chiefly the coarse Syene granite) of statues, of obelisks, of por- 

 tions of the temples, and of the facing of the pyramids, shows in 

 the greater number of cases noticeable disintegration. That 

 manifested by the statues is manifested chiefly as exfoliation of a 

 thin film, 0.5-0.7 cm. in thickness, from the pedestal, feet, and 

 lower portion of the legs. Above the knees, the original high polish 

 is commonly still intact, and tapping does not reveal incipient 

 exfoliation or flaking. Examples of this type of disintegration 

 can be seen on many, but not all, of the statues of Rameses II in 

 the Forecourt of the Temple of Luxor and by the statue of Rameses 

 II at the north entrance, by the colossal statue of Rameses II at 

 the entrance to the great Hypostyle Hall, Karnak (Fig. 3), and 

 by the medium-sized statue in the temple of Ptah, and by about 

 half the statues of the coarse red Syene granite and also those 

 of dark medium-grained rock possibly diorite in the museum at 

 Cairo. The statue in the Temple of Ptah is situated in a small dark 

 sanctuary and is not directly exposed to insolation. The other 

 statues at Luxor and Karnak are less well protected, but neverthe- 

 less are only very poorly exposed to the temperature changes con- 

 sequent upon solar heating. In the Great Temple of Karnak, 



