SURFACE GEOLOGY. 451 



Superior indicate that at one time the lakes may have been filled with 

 salt water from the arctic regions. 



The terraced valley Drift is known to extend far down the Ohio River. 

 Profs. E. W. Hilgard and F. V. Hopkins, in their geological researches 

 in the lower Mississippi valley, find in the Orange sand a wide out-spread 

 of gravel, pebbles, and occasionally small bowlders, which they connect 

 with the Drift of the northern States. Prof. Hopkins quotes the fact 

 of the elevation at which bowlders were found on high lands in the 

 Second Geological District of Ohio, as reported in the Report for 1869, as 

 showing that if these bowlders were transported by floating ice-rafts, as 

 he believed, and not by a vast, continuous northern glacier, the whole 

 district of the lower Mississippi was submerged in the Drift era, and by 

 these submerging waters the Drift materials he finds in the South could 

 readily have been transported. He gives a table of the elevations of the 

 higher lands in the path of such a great southern current to prove 

 that such high lands have all been beneath the water, and so were not 

 insuperable barriers to such a current. 



Prof. Hilgard writes: "The gravel is composed of northern rocks dis- 

 posed in belts, of which one occupies the main axis of the embayment, 

 while others mark outlets now closed ; and the extensive denudation and 

 violent plowing up of the more ancient formations clearly prove the 

 occurrence of an immense flow of waters southward, which, in the main 

 channels, moved pebbles of many pounds weight, while between them 

 the deposition of the finer materials took place in the more quiet waters. 

 That these events were not of a local character, that, on the contrary, 

 the phenomena observed in the southern States are but the necessary 

 consequences and complements of the Drift phenomena of the North, 

 hardly requires discussion ; but it is time that these facts were more gen- 

 erally understood and taken into the account by American geologists, 

 and that the Ohio should cease to be proclaimed as the southern limit of 

 the Drift." 



Westward of the State of Ohio the Drift is found in most of the west- 

 ern States. The State of Iowa I havecrossed on four different east and 

 west lines of railroad, and examined a large number of railroad cuts, 

 and every where I find evidences of Drift deposited and arranged by the 

 action of currents of water. Similar Drift phenomena appear under the 

 "Bluff" formation in the north-western part of Missouri, as reported by 

 Prof. G. C. Broadhead in the recent report of the geological survey of 

 that State. These many facts attest the submergence of a vast area, and 

 doubtless for a vast period of time, during which the bowlders and for- 

 eign rocks were brought in, and the bottom of the comparatively shallow 



