OUTLINES OF GEOLOGY. 67 



diluvium, and the lowest rocks of the inferior order. The 

 first of these may rest directly on the second, or the beds 

 which we have described as alluvial may be interposed. So 

 also, as in the island of New- York, the diluvium may rest 

 directly on the gneiss'; upon the highest formations of the su- 

 perior order; or upon any of the intermediate series. Of the 

 several formations, little or no doubt can exist that the supe- 

 perior order, and the coal measures, have been formed in ba- 

 sins of no great extent. There is also strong probability 

 that all the other formations, down to the slate of the inferior 

 order, have likewise been deposited in basins of greater mag- 

 nitude,"and that these greater basins have not always included 

 the lesser ones within their limits. The strongest proof of 

 this lies in the fact, that whole groups, series, and orders are 

 often wanting in places situated in countries where these 

 very formations exist at no great distance ; and there are 

 countries in which particular formations do not occur at all. 

 It might therefore appear at first to be liable to doubt, 

 whether the order in which we have ranked them is abso- 

 lutely correct, or whether some which are described as dif- 

 ferent in position may not be identical in age. No doubt, 

 however need remain, when the circumstances are fully in- 

 vestigated. 



(I.) By examining the strata at their outcrop on the ge- 

 neral surface, on the edges of deep ravines, or on the faces 

 of precipitous mountains ; by sinking wells and the shafts of 

 mines, the order of superposition of many of the formations 

 has been thoroughly determined. 



(2.) Although in places, or even in large districts, whole 

 formations, groups, or even orders, may be wanting, it has 

 never been observed that a stratified rock has been found 

 resting upon one that belongs to a higher place in the system 

 we have given. 



