44 WASTE AND RECONSTRUCTION. 



latitudes there are expanses of vast area and many feet in 

 depth entirely composed of decayed vegetation, and ready 

 to he converted into coal, like the analogous accumulations 

 of former epochs. In the animal world, on the other hand, 

 the coral-reef is perhaps the most striking instance of aggre- 

 gation by the minutest of means. Barely perceptible to 

 the naked eye, the tiny zoophyte, in countless myriads, 

 secretes the lime held in solution by the waters of the ocean, 

 till year after year and century after century the conjoint 

 structure so increases that at last the " reef " stretches away 

 many leagues in length and many fathoms in thickness. 

 As with coral-reefs so with beds of gregarious and drifted 

 shells, and so also with the enveloping limy and flinty 

 shields of microscopic organisms like the foraniinifera and 

 diatoms ; the former mere specks of animal jelly, the latter 

 mere points of plant-life, yet so increased by the immensity 

 of their numbers and the rapidity of their growth, that large 

 areas of the sea-bed as well as lakes and estuaries are thickly 

 strewn with their calcareous and siliceous envelopes. These 

 envelopes, though mere microscopic specks, are yet aggregated 

 in such myriads that they are capable of forming extensive 

 beds of limestone on the one hand, and of flinty rock on 

 the other. And such limestones and flint-rocks we find in 

 the solid crust, exhibiting to the eye of the microscopist 

 the beautiful organisms of which they are composed, and 

 proving that in former ages the earth's crust was built up 

 by the same agencies that still continue to remodel and up- 

 hold it. A great proportion of the chalk-rocks of England, 

 the nummulitic limestone that stretches from the Alps east- 

 ward through Europe and Asia on to the Philippine Islands, 

 and the mineral known as tripoli or polishing-slate, are 

 ancient strata formed by analogous microscopic organisms ; 

 and the same work still goes forward in the calcareous ooze 

 that covers so large an area of the Atlantic sea-bed, and in 



