ON A PIECE OF LIMESTONE. 171 



of the Eocene formation, the eai-liest of the tertiaries. We find this 

 limestone forming a heel of considerable thickness on the flanks of the 

 Pyrenees, and extending from tlie sliores of the Atlantic along the 

 south of France to the Al^js, in some parts of which it shows a thick- 

 ness of fifteen hundred feet, thence across to Asia Minor, Northern 

 India, and probably to the Pacific shore ; while another division of it 

 ranges along Northern Africa, and is especially noteworthy in Egypt, 

 where it rises into the hills that border the Nile for a loner distance 

 above Cairo, and furnishes the stone of which the Pyramids are built, 

 and out of which the Sphinx is carved. This stone not merely con- 

 tained numniuUtes, which are Foraminiferal shells much larger than 

 Globigeringe (sometimes attaining the size of a half-crown), but is en- 

 tirely made up of them, and of the fragments of those which have 

 been ground down by the action of the waves, as well as of other 

 shells inhabiting the same sea ; all cemented into a solid mass by the 

 process I shall presently describe. Another limestone of more limited 

 extent, belonging to the Eocene age, is found in the neighborhood of 

 Paris, and has furnished the material of which that beautiful city is 

 built. This is entirely made up of the minute Foraminiferal shells 

 termed 3Iiliolce, from their resemblance in size to grains of millet, and 

 is known as " miliolite limestone." So in Malta and in the neighbor- 

 hood of Vienna, there are limestones entirely composed of shells, 

 corals, and Foraminifera, which were formed in the Miocene or Middle 

 Tertiary period. And we have on the coast of Sufiblk the calcareous 

 bed known as the " coralline crag," to which equivalents are found in 

 various parts of Europe, that belongs to the Pliocene or Later Tei" 

 tiary period. The material of this bed is chiefly contributed by the 

 calcareous skeletons of composite animals that formerly ranked as 

 zo5phytes, but are now distinguished as Polyzoa. Although individu- 

 ally extremely minute, in fact microscopic, they have a very compli- 

 cated structure, allied to that of the lower Mollusks ; and they extend 

 themselves like trees by continuous budding, so that the fabrics they 

 form often have a stony solidity. They abound in our own seas, and, 

 as we shall presently find, they extend very far back in geological 

 time. 



Tlius, then, we see that, in the case of the Secondary and Tertiary 

 limestones, there can be no question of their production by the agency 

 of animals, which separated carbonate of lime from its solution in 

 sea-water, and formed it into corals, shells, etc., just as similar animals 

 are doing at the present time. And we have in these calcareous de- 

 posits many instances of local " metamorphism," which show that the 

 existence of a sub-crystalline, or even of a complete crystalline, ar- 

 rangement in the particles of carbonate of lime is no proof that the 

 materials of these deposits were not originally drawn from their solu- 

 tion by the agency which formed those whose organic origin is obvious. 

 Thus in the neighborhood of the Giant's Causeway, where volcanic 



