§ 45. STRATA COMPOSED OF ORGANIC REMAINS. 887 



subsidences of the land and irruptions of the ocean have 

 taken place — and the destructive and conservative influ- 

 ences of caloric and of water have been constantly exerted; 

 the phases of action have alone differed in duration and 

 intensity. 



" Ages have rolled their course,, and Time grown grey — 



The earth has gathered to her womb again, 



And yet again, the myriads that were born 



Of her uncounted, unremembered tribes. 



The seas have changed their beds — th' eternal hills 



Have stooped with age — the solid continents 



Have left their place — and Man's imperial works, 



The toil, pride, strength of kingdoms, which had flung 



Their haughty honours in the face of Heaven, 



As if immortal — have been swept away." 



HENRY WARE. 



45. Strata composed of organic remains. — In a 

 previous discourse (ante, p. 657), I dwelt upon the highly 

 interesting subject of the elaboration of calcareous and sili- 

 ceous strata from gaseous and fluid elements by vital action, 

 and the formation of islands and continents by the agency 

 of countless myriads of living instruments. Let us for a 

 moment consider how far the present mineral constituents 

 of the earth's crust have been derived from organized beings. 

 The strata of vegetable origin consist of peat, of forests 

 engulfed by subsidences of the land, or imbedded in the 

 silt and mud of rivers and deltas, or in the bed of the ocean 

 — of the lignite and brown coal of the tertiary deposits — 

 of the coals and shales of the carboniferous strata — and of 

 the silicified and calcified trunks of trees in the tertiary and 

 secondary formations. 



But the strata which consist wholly, or in a great mea- 

 sure, of animal exuviae, are so numerous, and of such pro- 

 digious extent, that the interrogation of the poet may be 

 reiterated by the philosopher — 



" Where is the dust that has not been alive ?" 



