6 INTRODUCTION. 



increase in extent ; how they are often continued out scores of miles beneath the 

 sea, as the bottom of the shallow shore-waters ; and that these submerged beds are 

 formed through constant depositions from the ever-moving waters. Then we go 

 among the hard rocks, and find strata made of sand in irregular layers, much like 

 those of the beach ; and on opening some of the layers we discover ripple-marks 

 covering the surface, as distinct and regular as if just made by the waves ; or, in 

 another place, we find the strata made up of regular layers of sand and clay alter- 

 nating, such as form from the gradual settling of the muddy material emptied into 

 the ocean by rivers, — or, in another place, layers of rounded, water-worn pebbles, 

 such as occur beneath rapidly-moving waters, whether of waves or rivers. We 

 remark that these hard rocks differ from the loose sand, clay, or pebbly deposits 

 simply in being consolidated into a rock. Then, in other places, we discover these 

 sand-deposits in all states of consolidation, from the soft, movable sand, 

 through a half-compacted condition, to the gritty sandstone ; and, further, we 

 discover, perhaps, the very means of this consolidation, and see it in its pro- 

 gress, making rock out of sand or clay. By such steps as these the mind is 

 borne along irresistibly to the conclusion that rocks were slowly made through 

 commonplace operations. 



"We may see, on another sea-shore, extensive beds of limestone forming from 

 shells and corals, having as firm a texture as any marble ; we may watch the 

 process of accumulation from the growth of corals and the wear of the waves, 

 and find the remains of corals and shells in the compact bed. If we then meet 

 with a limestone over the continent containing remains of corals, or shells, no 

 firmer, not different in composition, but every way like the coral reef-rock, or 

 the shell-rock of other regions, the mind, if allowed to act at all, will infer 

 that the ancient limestone was as much a slowly-formed rock, made of corals, 

 or shells, as the limestone of coral seas. 



In a volcanic district, we witness the melted rock poured out in wide-spread 

 layers and cooling into compact rock, and learn, after a little observation, that 

 just such layers piled upon one another make the great volcanic mountain, 

 although it may be 10,000 feet in height. "We remark, further, that the frac- 

 tured crust in those regions has often let out the lava to spread the surface 

 with rock, even to great distances from the crater. 



Should we, after this, discover essentially the same kind of rock in wide- 

 spread beds, and trace out the fractures filled with it, leading downward 

 through the subjacent strata, as if to some seat of fires, and discover marks of 

 fire in the baking of the underlying beds, we use our reason in the only legiti- 

 mate way when we conclude that these beds were thrown out melted, even 

 though they may be far from any volcanic centre. 



If we see skeletons buried in sand and clay that we do not doubt are real 

 skeletons of familiar animals, and then in a bed of rock discover other skele- 

 tons, but of unfamiliar animals, yet with every bone a true bone in form, tex- 

 ture, and composition, and every joint and limb modelled according to the plan 

 in known species, we pass, by an unavoidable step, to the belief that the last is 

 a relic of an animal as well as the former, and that it lies in its burial-place, 

 although that burial-place be now the solid rock. 



These few examples elucidate the mode of reasoning upon which geological 

 deductions are based. 



