374-Mr Weaver's Vieiso o/Ehrenberg's Observations XL. — On the Composition of Chalk Rocks and Chalk Marl by invisible Organic Bodies : from the Observations of Dr. Ehrenberg, By Thomas Weaver, Esq,, F.R.S,, F.G.S., M.R.I.A, Sfc, Sfc, [Concluded from p. 315.] On the Composition of the Compact Limestone of Upper Egypt and Arabia by the invisible Animalcules of the White Chalk of Europe. Both the nummulite limestone of the pyramids of Geza on the left bank of the Nile, and the same kind of rock on the right bank near Cairo, contain numerous microscopic ani-malcules of the chalk, which serve as a cement to the Num-mulites. 1 had often examined microscopically specimens which I had brought from thence, but I did not succeed in separating and rendering visible the different elements with equal cleiirness, until I applied my newly-acquired practice, which was much facilitated by immersing these stones a longer time in water. The same result attended the examination of the other calcareous rock masses of Upper Egypt and Arabia, showing that the animalcules of the chalk occupy in a sur-prising manner a wide extent of country in Libya. Nummulite limestone, wherever occurring, has been most usually referred to the tertiary period, although perhaps often belonging to the chalk. In Egypt it possesses no great ex-tent. On the right bank of the Nile it is deposited only in the small hills near Cairo, and on the left bank, as it appears, in a tract extending from Siout to the declivity of the com-pact limestone, which latter constitutes the mass of the rocks that line the course of the Nile in Upper Egypt. It forms the foundation and principal material of the Pyramids. North-ward it is directly bordered by the slimy delta of the Nile, the productive soil of Egypt. Between the Oasis of Jupiter Am-mon and the Mediterranean, is a wide elevated plateau or table-land of rock, among whose numerous organic remains are known tertiary forms. The whole of Upper Egypt, as far as Syene, has a similar character. In 1828, though assured that its limestone rocks were more ancient than the tertiary period, yet, from want of distinct fossils, I was doubtful whether they might not be referred to the Jura formation. On the south, and not far from Syene, this limestone is in-cumbent on sandstone (Quadersandstein ?), and the two repose on granite and the primary rocks connected therewith. I gave these views in 1828 in the geologically coloured map which accompanied the first section of the first volume of my Travels in Egypt, Libya, Nubia, and Dongola. It now results, from the microscopic examination which has
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