. The microscope and its revelations. e chief partis made up of the shells of f i/t/n-rina. a marine form of entomo-stracous crustacean. Different specimens of chalk vary greatly in I08S THE MICROSCOPE IN GEOLOGICAL INVESTIGATION the proportion which not only the distinctly organic remains bear tothe amorphous residuum, but also the different kinds of the formerbear to each other ; and this is quite what might be anticipated whenwe remember how one or another tribe of animals predominatesin the several parts of a large area; but it may be fairly concluded,from what has been already stated of t
. The microscope and its revelations. e chief partis made up of the shells of f i/t/n-rina. a marine form of entomo-stracous crustacean. Different specimens of chalk vary greatly in I08S THE MICROSCOPE IN GEOLOGICAL INVESTIGATION the proportion which not only the distinctly organic remains bear tothe amorphous residuum, but also the different kinds of the formerbear to each other ; and this is quite what might be anticipated whenwe remember how one or another tribe of animals predominatesin the several parts of a large area; but it may be fairly concluded,from what has been already stated of the amorphous component ofthe Gflobigerina-m\id, that the amorphous constituent of chalk like-wise is the disintegrated residuum of foraminiferal shells, or at anyrate of some small calcareous organism. But, further, the Globig&rinarmud now in process of formation is in some places literally crowdedwith sponges having a complete silicious skeleton ; and some of thembear such an extraordinarily close resemblance, alike in structure. FIG. 812.—Microscopic organisms (chie&j foraminifera) in chalk from Meudoii,seen partly as opaque, and partly as transparent objects. and in external form, to the Yv the microscopic examination of All these correspondencesshow that the formation of chalk took place under conditionsessentially similar to those under which the deposit of Globiyerina-irmd is being formed over the Atlantic sea-bed at the present examining chalk or other similar mixed aggregations, whose 1 On the Organii Origin of the so-called Crystalloids of Chalk in Ann. ser. iii. vol. viii. iMIil, pp. l!l:!-200. Murray and Knurd, I >ii/> ,SV<i Deposits(Challenger Jlrp
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