1864.1 467 [Lesley. 



tinguished; the one stratified in the same sense as the Silurian lime- 

 stones themselves ; the other a surface-wash over the basset edges of 

 the first. The date of the formation of this local surface-wash may 

 be tertiary, and perhaps post-tertiary. The stratified portions must 

 be, as to their stratification, of Lower Silurian age ; while the meta- 

 morphism which they have undergone, in situ, productive of strati- 

 fied clays and ores, 7na^ date from an?/ time subsequent to the forma- 

 tion of a surface topographi/ ajjproximately identical with that 

 lohich 7101V exists. The actual change of the original Lower Silurian 

 calcoferriferous sandstones and slates, in situ, at their outcrops, into 

 limonite clay beds, in ipso situ, stratified as before, but charged with 

 an additional percentage of the oxides from a former higher surface 

 now eroded, and with this extra charge of iron and manganese car- 

 ried by percolation down to and crystallized against their foot rock, — 

 this change may have required an immen.se time to perfect, and no 

 doubt was going on, pari passu with the degradation of the surface 

 by slow erosion, from higher to lower levels, until it stands at the 

 level of the present day. 



This long era of iron ore concentration, in the Lower Silurian 

 slates, could not have commenced until after the close of the coal 

 era; and I will be able to show, I think, not until after the close of 

 the New Red or Middle Secondary age. It may have been commen- 

 surate with the Cretaceous, Tertiary and Recent periods together ; or 

 with the Tertiary or the latest Tertiary and Recent alone. But it 

 seems more likely, in view of the geographical relationships of the 

 New Red to the Silurian on one side of it, and to the Cre- 

 taceous on the other side of it, that the erosion of the surface 

 commenced at the close of the New Red era, and continued with- 

 out intermission down to the present day. There is no sufiicient 

 evidence of the submergence of the x\tlantic side of the Continent, 

 since its emergence after the coal. There is not a trace of New Red, 

 Cretaceous, or Tertiary deposit recorded by any geologist, so far as I 

 am aware, over all the country back of the Great Barrier range, from 

 west of the Hudson, until we reach the prairie lands of the Mississippi 

 Valley. There were, of course. New Red rivers. Cretaceous brooks, 

 Tertiary freshets. Glacial ice ; but these carved out the present sur- 

 face-topography of the Appalachians, without leaving a plant, an ani- 

 mal, or even a pebble which can be recognized as belonging to any 

 special age. In fact, the New Red surface must have been largely 

 remodelled, lowered, and denuded of New Red relics, by the Creta- 

 ceous agents; and the same liberties were no doubt taken with the 



