39° 



DONALD C. BARTON 



exposed surfaces a very marked exfoliation to the depth of o . 5 to 

 0.8 cm. Minor exfoliation, in addition, is found along the joints 

 between the blocks. Exposed surfaces not exfoliating commonly 

 show marked granular flaking. The orientation of the surface, with 

 north, cast, south, or west exposure, does not seem appreciably to 

 affect the intensity of the disintegration and exfoliation. Disinte- 

 gration and exfoliation are shown also by the granite facing that 

 extends for 30 ft. down the shaft on the north side of the second 

 pyramid, by the granite pavement of the temple at the east base 

 of the second pyramid, and by the granite blocks immediately to 

 the north of the east entrance to the temple. A striking feature 



Fu:. 4. -Diagrammatic sketch showing the greater degree of disintegration 

 below the old soil line than above. East entrance to the temple of the second 

 pyramid, Gizeh. 



in this latter case, as can be seen from the accompanying sketch 

 (Fig. 4) , is that the disintegration is distinctly stronger below what 

 seems to have been an old soil line than above it. A similar case 

 was noted at one of the pyramids at Sakkara. The debris resulting 

 from the disintegration and exfoliation in all these shows slight 

 but megascopically noticeable decomposition. The degree of the 

 alteration of the colored silicates is greater than that of the feld- 

 spars, and that of the plagioclase is greater than that of the ortho- 

 clase. 



The pyramids of Gizeh date from the Fourth Dynasty, about 

 2850-2700 B.C., the statues of Rameses II at Karnak and Luxor 

 date from the Nineteenth Dynasty, 1 292-1 225 B.C., and the Granite 

 Sanctuary, Karnak, dates from the reign of Phillip Arrhidaeus, 

 318 B.C. The average rate of disintegration and exfoliation would 

 therefore seem to be about 1 cm. to o. 5 cm. in five thousand years. 



