170 THE POPULAR SCIENCE MONTHLY. 



you have a splendid illustration of the great Oolitic formation, which 

 is almost entirely made up of calcareous deposits that can be clearly 

 traced to an animal origin, although their condition is now very dif- 

 ferent. The Coral Rag of Oxfordshire is an old coral-reef that has 

 undergone very little change, consisting of fossil corals, and of the 

 shells, crinoids, etc., that lived on the reef. And the " freestones " 

 of Bath and Portland are mainly composed of the fine sand which 

 was formed by the wearing-down of similar reefs, of which the re- 

 mains are found here and there. The name " oolite " or roe-stone, is 

 given to the whole formation, on account of the resemblance in texture 

 borne by some of its characteristic members to the roe of a fish ; but 

 this " oolitic " structure is not peculiar to the Oolitic formation, being 

 found in other limestones, as I shall presently point out to you. A 

 very curious example of the " metamorphic " action by which the 

 texture of a calcareous rock may be so completely altered as to con- 

 ceal its origin is aflibrded, by the fact that the beautiful Carrara marble, 

 which is used for statuary, belongs to the Oolitic formation. If this 

 metamorphisra, the nature of which I shall presently explain, proceeds 

 further, it will produce large crystals of calc-spar ; and I remember 

 that Mr. Baily, the sculptor of the beautiful statue of " Eve at the 

 Fountain," which is in your Fine Arts Gallery, was greatly embar- 

 rassed by a vein of calc-spar that ran through the block from which 

 he cut it, and had to let a patch of marble into Eve's back. The next 

 great calcareous formation above the Oolite is the Chalk, the material 

 of which is exactly the same as that of limestone, although its texture 

 is so different. Our deep-sea researches have entirely confirmed the 

 opinion which had been previously formed on the basis of microscopic 

 research, that the whole of the enormous mass of Chalk now raised 

 up into the cliffs and downs of the southern portion of England was 

 formed on the bed of the ocean, by the agency of animals chiefly the 

 minute Foraminifera, which separate carbonate of lime from the sea- 

 water as the material of their shells ; just as successive generations 

 of fresh- water mussels living in a lake form a bed of calcareous marl 

 on its bottom by the decay of their shells, which sets free in a solid 

 form the lime they have taken from the water that poured it into the 

 lake in solution. We have brought up by the hundred-weight, from 

 depths of three miles in the Atlantic, a white mud, which, when 

 dried, exactly resembles chalk ; and this, when examined with the 

 microscope, is found to consist partly of perfect shells of minute 

 Globigerince, of which many hundreds would only weigh a grain, 

 and partly of what we call Globigerina ooze, which is obviously the 

 product of the decay of former generations of similar shells. 



In the Tertiary or Neozic (modern life) series, we find many lime- 

 stone deposits of considerable importance, but none so vast as those 

 to which I have previously drawn your attention. The most extensive 

 is the " nummulitic limestone," which is one of the oldest members 



