294 GENERAL OBSERVATIONS. 



petrifaction ; and even among our ironstones, or ferruginous balls, we 

 have found some in the state of soft ochre, while others ai-e in a hard 

 metallic form. It is not easy to investigate the causes of these diifer- 

 ent degrees of induration; but we may safely state, that they have 

 not originated in any extrinsic agency, operating either from below 

 or from above. Had the consolidation proceeded from below, we 

 should have found the hardest beds lowest; had it proceeded from 

 above, the order must have been reversed; but as we find the 

 hard and soft strata alternating, without observing any such grada- 

 tion, we must look for the reason of this diversity in the original 

 qualities of the substances composing the strata, their chemical 

 affinities and attractions, or similar causes operating about the era of 

 their deposition. The structure of some of the beds might be influen- 

 ced by those immediately over them; for we have noticed (p. 115), 

 that the blue limestone appears to have sent down a large portion of 

 calcareous matter into the sandstone that succeeds it. Some time 

 may have been requisite to complete the consolidation of the hard 

 beds ; but time alone has not effected the cheinge ; for the softer strata 

 cannot be inferior in age to the compact beds with which they alternate. 

 13. Our strata cannot have been formed at the bottom of a 

 former ocean, in the same gradual way in which the earthy sediment, 

 brought down by the rivers or detached from the shore, is now de- 

 posited in the bottom of the sea. — It is the opinion of many geologists, 

 that our present strata have resulted from the gradual demolition of 

 more ancient strata, the materials of which, being washed away by 

 the rains and streams, were deposited in the bottom of an ancient 

 ocean ; and that, through the effect of a supposed central fire or heat, 

 in the interior of the globe, they were consolidated, and then raised 

 up to form our present dry land. Such authors assert, that the same 

 process is now going forward ; the spoils of our present strata, carried 

 down by rivers, or detached from the shore, being deposited in 



