. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palaeontological science. Paleontology. THE FOSSILIFEROUS ROCKS. 29 more or less abundant calcareous matrix. When the grains are pretty nearly spherical and are in tolerably close contact, the rock looks very like the roe of a fish, and the name of " oolite " or " egg-stone " is in allusion to this. When the grains are of the size of peas or upwards, the rock is often called a " pisolite " (Lat. pisum, a pea). Limestones having this peculiar structure are especi
. The ancient life-history of the earth; a comprehensive outline of the principles and leading facts of palaeontological science. Paleontology. THE FOSSILIFEROUS ROCKS. 29 more or less abundant calcareous matrix. When the grains are pretty nearly spherical and are in tolerably close contact, the rock looks very like the roe of a fish, and the name of " oolite " or " egg-stone " is in allusion to this. When the grains are of the size of peas or upwards, the rock is often called a " pisolite " (Lat. pisum, a pea). Limestones having this peculiar structure are especially abundant in the Jurassic formation, which is often called the " Oolitic series " for this reason; but essentially similar limestones occur not uncom- monly in the Silurian, Devonian, and Carboniferous forma- tions, and, indeed, in almost all rock-groups in which limestones are largely developed. ^Vhatever may be the age of the for- mation in which they occur, and whatever may be the size of their component "eggs," the structure of oolitic limestones is fundamentally the same. All the ordinary oolitic limestones, namely, consist of little spherical or ovoid " concretions," as they are termed, cemented together by a larger or smaller amount of crystalline carbonate of lime, together, in many instances, with numerous organic remains of different kinds (fig. 13). When examined in polished slabs, or in thin sec- tions prepared for the micro- scope, each of these little con- cretions is seen to consist of numerous concentric coats of carbonate of lime, which some- times simply surround an ima- ginary centre, but which, more commonly, have been suc- cessively deposited round some foreign body, such as a little crystal of quartz, a clus- ter of sand-grains, or a minute shell. In other cases, as in some of the beds of the Car- boniferous limestone in the North of England, where the limestone is highly " arenaceous," there is a modification of
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Keywords: ., bookcentur, bookdecade1870, booksubjectpaleontology, bookyear1876
