of the Lafayette Formation. 40 1 



has called special attention and which, in part at least undoubt- 

 edly fall within the Lafayette proper, such grass and sedge 

 vegetation is all that is indicated. It argues, during the sub- 

 aerial exposure admitted on all hands, a more rigorous climate 

 than is consistent with our knowledge of even late Tertiary 

 times ; we are reminded of subarctic bogs, not of subtropic 

 forests. It is in connection with such bog vegetation too, I 

 think, that the process of ferrugination that is so conspicuous 

 within the Lafayette, and has even given rise to iron ore 

 deposits, is to be explained. It is obvious that the solutions 

 which subsequently oxidized into limonite incrustations and 

 ferruginous sandstone ledges, must have been of the same 

 character as those now forming similar deposits in our northern 

 latitudes ; e. g. in Oregon and Washington, where under the 

 influence of a cool, moist climate, limonite deposits and fer- 

 ruginous sandstones are forming under our very eyes, from the 

 seepage and drippings of the dense and ever moist covering of 

 moss and grasses, percolating through more or less ferruginous 

 surface beds and impregnating all pervious formations underly- 

 ing, with what ultimately becomes a limonite cement for sands 

 and sandy clays. A similar vegetative covering, with its concomi- 

 tant reduction of the ferric hydrate resulting from the decom- 

 position of hornblendic and other iron-bearing materials of the 

 moraine sands, would naturally have covered the Lafayette sur- 

 face when left free from overflow ; and would explain the promi- 

 nent ferrugination, as well as the fact that the minute grains 

 of clay which we so frequently find intermixed with the quartz 

 sand are so commonly, in contrast to the latter, decidedly 

 angular, and have manifestly not undergone any sensible attri- 

 tion. I conceive these clay-particles to be the result of kao- 

 linization in place, under the influence of the carbonic acid 

 solutions which evidently have been so very active within the 

 entire formation as to leave little or nothing behind that is 

 still subject to weathering, or carbonate solution. 



I have in the foregoing discussion designedly confined my- 

 self to the ground with which I am familiar — The " Orange- 

 Sand Delta " in and contiguous to the Mississippi Embayment ; 

 both because its phenomena are most familiar to me, and 

 because I believe that, as previously stated, its development 

 may have been largely independent of the events that happened 

 beyond the Appalachian axis of upheaval and the Archsean 

 highlands. How far such assumption may be compatible with 

 the evidence in the possession of McGee, as regards the inter- 

 vening ground in Georgia and farther east, the publications 

 thus far made by him are insufficient to determine. But so 

 far as they have been published, I cannot reconcile the litho- 

 logical, stratigraphical and (negative) paleontological charac- 



