. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palaeontological science. Paleontology. THE FOSSILIFEROUS ROCKS. 27 thereby. Thus, in Hmestones which have been greatly altered or " metamorphosed'' by the combined action of heat and pres-. Fig. II. — Section of Carboniferous Limestone from Spergen Hill, Indiana, , showing numerous large-sized Foramiiiifera {Endothyra) and a few oolitic grains ; magnified. (Original.) Fig. 12.—Section of Coniston Limestone (Lower Silurian) from Keisley, Westmore- land; magnified. The matrix is very
. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palaeontological science. Paleontology. THE FOSSILIFEROUS ROCKS. 27 thereby. Thus, in Hmestones which have been greatly altered or " metamorphosed'' by the combined action of heat and pres-. Fig. II. — Section of Carboniferous Limestone from Spergen Hill, Indiana, , showing numerous large-sized Foramiiiifera {Endothyra) and a few oolitic grains ; magnified. (Original.) Fig. 12.—Section of Coniston Limestone (Lower Silurian) from Keisley, Westmore- land; magnified. The matrix is very coarse- ly cr^^stalline, and the included organic re- mains are chiefly stems of Crinoids. (Ori- ginal.) sure, all traces of organic remains become annihilated, and the rock becomes completely crystalline throughout. This, for example, is the case with the ordinary white "statuary marble," slices of which exhibit under the microscope nothing but an aggregate of beautifully transparent crystals of carbonate of lime, without the smallest traces of fossils. There are also other cases, where the limestone is not necessarily highly crystalline, and where no metamorphic action in the strict sense has taken place, in which, nevertheless, the microscope fails to reveal any evidence that the rock is organic. Such cases are somewhat obscure, and doubtless depend on differ- ent causes in different instances; but they do not affect the important generalisation that limestones are fundamentally the product of the operation of living beings. This fact remains certain ; and when we consider the vast superficial extent occupied by calcareous deposits, and the enormous collective thickness of these, the mind cannot fail to be impressed with the immensity of the period demanded for the formation of these by the agency of such humble and often microscopic creatures as Corals, Sea-lilies, Foraminifers, and Shell-fish. Amongst the numerous varieties of limestone, a few are of such in
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Keywords: ., bookcentur, bookdecade1870, booksubjectpaleontology, bookyear1876
