382 CONCLUDING REMARKS. [Ch. XXVI. 



cessive periods, has extended over a subterranean space equal 

 at least in area to the present European continent, and often 

 through a portion of the earth's crust 4000 feet or more in 

 thickness. 



The principal effect of these volcanic operations in the nether 

 regions, during the tertiary periods, or since the existing species 

 began to flourish, has been to heave up to the surface hypogene 

 formations of an age anterior to the carboniferous. We 

 imagine that the repetition of another series of movements, of 

 equal violence, might upraise the plutonic and metamorphic 

 rocks of many of the secondary periods ; and if the same force 

 should still continue to act, the next convulsions might bring 

 up the tertiary and recent hypogene rocks, by which time we 

 imagine that nearly all the sedimentary strata now in sight 

 would either have been destroyed by the action of water, or 

 would have assumed the metamorphic structure, or would have 

 been melted down into plutonic and volcanic rocks. 



At the close of this chapter the reader will find a table of 

 the chronological relations of the principal divisions of rocks 

 according to the views above set forth. The sketch is con- 

 fessedly imperfect, but it will elucidate our theory of the con- 

 nexion which may exist between the hypogene rocks of different 

 periods, and the alluvial, volcanic, and sedimentary formations. 

 A second table is added, containing the names of some of the 

 principal groups of sedimentary strata mentioned in this work, 

 arranged in their order of superposition. 



Concluding Remarks. In our history of the progress of 

 geology, in the first volume, we stated that the opinion 

 originally promulgated by Hutton, < that the strata called 

 primitive were mere altered sedimentary rocks,' was vehe- 

 mently opposed for a time, the main objection to the theory 

 being its supposed tendency to promote a belief in the past 

 eternity of our planet. Previously the absence of animal 

 and vegetable remains in the so-called primitive strata, had 

 been appealed to, as proving that there had been a period when 

 the planet was uninhabited by living beings, and when, as was 



