VALLEY OF THE OHTO, 135 



constitute the bouiulary of this debris. Beyond that river, 

 tliere are iiifleed l)ut lew water worn pebbles of anjf kind ; 

 and tiie narrow alluvions of the streams are generally argil- 

 laceous. I have travelled over most of the northern and 

 north-eastern parts of Kentucky, and do not now recollect 

 to have seen any foreign rolled pebbles. Mr. Warren has 

 visited the north-western portions of the same State, and at 

 my request was particularly attentive to this point, but did 

 not discover any. The acute and observing Mr, Nuttall 

 travelled througli tlic centre of the same State from north 

 to soutli on foot, but after leaving the valley of the Ohio op- 

 posite this town, he found none of these fragments until he 

 approached the French Broad, in Tennessee, whose source is 

 in a jirimordial formation. To the west and south-west, the 

 currents of the great valley have transported the debris 

 much farther. Mr. Nuttall has tiaced it only to the mouth 

 of the river St. Fiancois ; but my late lamented friend Dr. 

 Goforth met with it in tlie form of gravel, not many miles 

 al)ove Natchez. To the north-west, it was found by Mr. 

 Nuttall on the Missouri, as far as the great bend at the Man- 

 dan villages, beyond which he did not ascend. From the 

 mouth of tins river to Erie in Pennsylvania, the same perse- 

 vering naturalist met with it on the shores of all the rivers 

 and lakes which he visited, and from the information which 

 he has kindly afforded me by letter, it appears that this de- 

 bris is largei- and in greater quantities in that region than 

 this. Witliin the limits here sketclied, it is found in the vi- 

 cinity of all the streams, and forms with the ruins of the sur- 

 rounding strata the bases of all the fertile and level prairies. 

 We are hence. I think, justified in the conclusion, that its 

 origin was in tiie north, and tiiat it was brou<!;ht and depo- 

 sited on the surface of this country by currents which in an- 

 cient times flowed from beyond the lakes to the Gulf of 

 Mexico, and of which it may be regarded as the sign and 

 effect. 



A more recent formation than many of the alluvial l)eds 

 contained within tlic limits just defined, is tlie stratum of loam 



