Mr. L. Horner on the Alluvial Land of Egypt. 225 



established. The average observed angles between the conjugate 



axes of these four systems of planes are 89° 1 1', 91° 52', 91° 20', and 



90° 30' respectively; and the bearings of their cleavage planes are — 



Cleavage. Faults. 



7° 46' North of East. 7° 30' North of East. 



33° 3 1 ' North of East. 34° 22' North of East. 



30° 30' South of East. 



10° South of East. 



The cleavage planes are distinguished from the joint planes by a 

 peculiar flaggy or platy structure developed in the rock-mass, parallel 

 to their direction. This structure the author thinks to be the result 

 of pressure ; and that it indicates that the cleavage planes are per- 

 pendicular to the lines of maximum force ; he considers the cleavage 

 planes to have been developed while the rock was yet soft. The 

 joint planes, on the contrary, which are conjugate to the cleavage 

 planes, are considered as perpendicular to the lines of minimum 

 force of compression ; they were formed by the shrinking of the rock 

 mass, were subsequent to the cleavage planes, and formed when the 

 rock was hard. 



Having established the geometrical relations of the structural planes 

 of the conglomerate, the author then deduces from them the mecha- 

 nical forces which have been at work in bringing the district to its 

 present condition and form. He believes that the method he has 

 adopted in reference to the conglomerate of the county of Waterford 

 is applicable to the physical structure of other districts ; and that 

 his results, if confirmed by corresponding results in other districts, 

 of which he is confident, will prove to be a substantial addition to 

 the arguments in favour of the mechanical theory of slaty cleavage. 



Feb. 1 1 . — Major-General Sabine, R.A., Treas. and V.P., in the 

 Chair. 



The following communication was read : — 



" An Account of some recent Researches near Cairo, undertaken 

 •with the view of throwing light upon the Geological History of the 

 Alluvial Land of Egvpt." — Part. II. By Leonard Horner, Esq., 

 V.P.R.S. 



In the first part of this Memoir, read on the 8th of February, 1855, 

 the author stated the main object of the inquiry to have been, to endea- 

 vour, by probing the alluvial land in appropriate places, to discover 

 the probable time that has elapsed since the lowest layer of Nile 

 sediment was deposited, and thus to connect geological and historical 

 time. This object, in the opinion of the author, can only be at- 

 tained by means of shafts and borings of the soil in the immediate 

 neighbourhood of monuments of a known age. Tiie places he selected 

 for these excavations were the vicinity of the Obelisk of Ilcliopolis, 

 and the site of ancient INIemphis. The general introductory matter, 

 and the analyses of the various soils penetrated, together with a 

 description of the researches at Ileliopolis, are given in the first part 

 of the memoir ; but the author deferred his general conclusions, and 

 all inferences as to the secular increase of the alluvial deposits, until 

 he should have an opportunity of laying before the Society an account 



Phil. May. S. 4. Vol. 10. No. 106. Hept. 1858. Q 



