THE MICROSCOPE IN GEOLOGICAL INVESTIGATION. 309 



or the shells of Mollusks. In the formation of the Coralline Crag' (Ter- 

 tiary) of the eastern coast of England, Polyzoaries ( 548) had the 

 greatest share; but the Tertiary limestone of which Paris is chiefly built 

 consists almost exclusively of the shells of Miliolida ( 462), and is thus 

 known as Miliolite (millet-seed) limestone. In the vast stratum of Nu- 

 mulitic limestone (Fig. 333), which was formed at the commencement 

 of the Tertiary period, the Microscope enables us to see that the matrix 

 in which the large entire Nummulites are imbedded, is itself composed 

 of comminuted fragments and young of the same, together with minuter 

 Foraminifera. In the Oolitic (Secondary) formation, again, there are 

 many beds which are shown by the Microscope to have been chiefly com- 

 posed of Foraminiferal shells; and in those portions which exhibit the 

 ' roe-stone ' arrangement from which the rock derives its name (such as is 

 beautifully displayed in many specimens of Bath-stone and Portland- 

 stone), it is found by Microscopic examination of transparent sections, 

 that each rounded concretion is composed of a series of concentric 

 spheres formed by successive calcareous deposits upon a central nucleus, 

 which nucleus is often a Foraminiferal shell. In these and similar calca- 

 reous formations, the entire materials of which were obviously furnished 

 by the accumulation of animal remains, it not unfrequently happens 

 that all traces of their origin are obliterated by local ' metamorphic ' 

 action usually dependent upon neighboring Volcanic heat; and thus a 

 crystalline marble, whose particles present not the least evidence of or- 

 ganic arrangement, may have been formed by the metamorphosis of 

 Chalky, Oolitic, or Nummulitic limestone. INow there is very strong evi- 

 dence that the vast mass of sub-crystalline ' Carboniferous ' limestone, 

 which forms our coal-basins, has had a similar origin in Foraminiferal 

 and Zoophytic life; the traces of which have been for the most part re- 

 moved by the metamorphic action involved in its upheaval. For where 

 it has sustained but little disturbance, the evidences of its organic 

 (chiefly Foraminiferal) origin are unmistakable. Thus in the great 

 plains of Russia, there are certain bands of limestone of this epoch, vary- 

 ing in thickness from fifteen inches to five feet, and frequently repeated 

 through a vertical depth of two hundred feet over very wide areas, which 

 are almost entirely composed of the extinct genus Fusulina (Fig. 331). 

 Again, those parts of the Carboniferous limestone of Ireland which have 

 undergone least disturbance, can be plainly shown, by the examination 

 of Microscopic sections, to consist of the remains of Foraminifera, Poly- 

 zoa, fragments of Coral, etc. And where, as not unfrequently happens, 

 beds of this limestone are separated by clay seams, these are found to 

 be loaded with ' Microzoa ' of various kinds, particularly Foraminifera 

 (of which the Saccamina, Fig. 319, a, has come down to the present 

 time), and the beautiful Polyzoaries known as 'lace-corals.' 



702. Mention has been already made (487 note) of Prof. Ehrenberg's 

 very remarkable discovery, that a large proportion (to say the least) of 

 the green sands which present themselves in various stratified deposits, 

 from the Silurian epoch to the Tertiary period, and which in certain 

 localities constitute what is known as the Greensand formation (beneath 

 the Chalk), is composed of the casts of the interior of minute shells of 

 Foraminifera and Mollusca, the shells themselves having entirely disap- 

 peared. The mineral material of these casts has not merely filled the 

 chambers and their communicating passages (Fig. 328, A, B), but has 

 also penetrated, even to its minutest ramifications, the canal-system of 

 the intermediate skeleton (Figs. 332, 337). The precise parallel to these 



