The microscope and its revelations . s of Nummulites, as in Nonionina, theinvesting layers of the successive whorls are in immediatecontact with those that have preceded them, instead of beingseparated, as in Eig. 337, by spaces prolonged from the cavi-ties of the chambers. 449. The same Nummulitic limestone also contains, incertain localities (as the South-west of Erance, ^^^- 3^- North-eastern India, &c.)a vast abundance of dis-coidal bodies termed Or-bitoides, which are so si-milar to Nummulites asto have been taken forthem, but which, whilestill Eoraminiferous, areformed upon a plan ofstru
The microscope and its revelations . s of Nummulites, as in Nonionina, theinvesting layers of the successive whorls are in immediatecontact with those that have preceded them, instead of beingseparated, as in Eig. 337, by spaces prolonged from the cavi-ties of the chambers. 449. The same Nummulitic limestone also contains, incertain localities (as the South-west of Erance, ^^^- 3^- North-eastern India, &c.)a vast abundance of dis-coidal bodies termed Or-bitoides, which are so si-milar to Nummulites asto have been taken forthem, but which, whilestill Eoraminiferous, areformed upon a plan ofstructure altogether dif-ferent. On account of theminuteness of their parts,and the completeness oftheir fossilization, theirstructure can only beelucidated by sectionsthin enough to be ex-amined by the micro-scope with transmittedlight; and it is conse-quently to the assistanceafforded by this instru-ment, that we are in-debted for our knowledgeof the curious type of or-ganization which it presents. When one of these disks (which3c. Section of Orhitoides Prattii, parallel tothe surface; traversing at a, a, the super-ficial layer, and at b, b, the median layer. 754 MICROSCOPIC GEOLOGY. vary in size, in different species, from that of a four-penny pieceto that of half a crown) is rnbbed-down so as to display its in-ternal organization, two different kinds of structure are usuallyseen in it; one being composed of chambers of very definiteform, quadrangular in some species, circular in others, arrangedwith a general but not constant regularity in concentriccircles (Kgs. 340, 341, h, b); the other, less transparent,being formed of minuter cells which have no such constancyof form, but which might almost be taken for the pieces of adissected-map (Figs. 340, 341, a, a). In the upper and lower Fig. 341.
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