BY THE ROCKY WALL. 65 



sediments never have so wide an extent as the strata which 

 underlie a continent; nor are they generally so evenly bedded 

 as our ordinary rock-strata. We must conclude, therefore, 

 that the watery action which arranged the sediments from 

 which our rock-strata have been formed, was a very widely 

 operating action. There is no watery action known sufficiently 

 wide-spread except the action of the ocean. In the ocean, 

 sediments are now settling down in sheets a thousand miles 

 broad. This conclusion is a somewhat startling one. It im- 

 plies that, wherever rocky strata exist, there the ocean's waters 

 have stood. Rocky strata are found hundreds of feet above 

 the level of the ocean, and the fact seems incompatible with 

 our conclusion. The average level of all the northern and 

 northwestern states is from six hundred to a thousand feet 

 above the sea. If the underlying strata were deposited by 

 the ocean, then either the ocean has greatly subsided in later 

 times, or regions which were once sea-bottom have been ex- 

 tensively uplifted. 



These subjects have attracted the attention of thoughtful 

 observers for a century indeed, for two or three centuries. 

 The question has been much discussed ; but no doubt is longer 

 entertained that the sea has covered all the land, and that the 

 exposure of land has resulted from upheaval of portions of 

 the ancient sea-bottom. Many confirmations of this view will 

 be discovered as we proceed. Thus by a very simple and easy 

 process of observation and reasoning we have reached a very 

 fundamental principle in geological science; and you under- 

 stand the evidence on which it rests. 



Now, if all the strata which underlie the land are formed 

 from marine sediments, the time required for their accumula- 

 tion must have been enormous. We have made observations 

 along the sea-shore, and have formed some conception of the 

 rate of sedimentation over a belt near the land. There are 

 times when violent winds cause the waves to wear down the 

 shore at such a rate that the sea, for a mile from shore, be- 

 comes turbid with sediments. This has been seen often at 

 Long Branch and Coney Island. But these periods are of 



6 



