810 



NOTES ON A MAP INTENDED TO ILLUSTRATE 



tacio-tertiary tidewater country, through which the rivers, which at first produced it, are 

 still flowing, and extending themselves, as they push forward their deltas, along the 

 present seaboard. Now, from this Appalachian belt, not from two to five thousand feet of 

 rocks, as in the case of the Coal Measures, but from twenty to thirty thousand feet of 

 superincumbent Upper Silurian, Devonian and Carboniferous measures have been swept 

 away, leaving the present floors of Lower Silurian rocks, which constitute the Great 

 Valley (of Winchester, Wythe, and Knoxville), and the other secluded anticlinal valleys 

 behind it. We seem to be restricted by these facts to the conclusion, that the erosion of 

 this Appalachian belt of upturned vertical or steep-dipping Devonian and Silurian out- 

 crops has furnished actually twice or thrice as great a mass of Cretaceous and Tertiary 

 detritus for the Atlantic waters as the Coal Measure areas of the Alleghany-Cumberland 

 plateau has been able to furnish to the great central estuary uniting the Polar Ocean with 

 the Gulf of Mexico in Cretaceous and Tertiary times. What became of all the subsequent 

 wastage which passed down the rivers during Middle Secondary times, — times during 

 which so much of the present Pacific side of the continent was formed : — how far it extends 

 beneath the Atlantic : — how much of it went to form the Central American deposits : — 

 how early began the Gulf Stream to sweep the western wastage round through Southern 

 Georgia and the Carolinas, northeastward, toward New England and Ireland, as it con- 

 tinues doing to-day: — and how much weight we must assign to the third element — the 

 cotemporaneous erosion of the great Azoic (Blue Ridge, South Mountain, Highland) 

 belt, which has always formed a barrier between the disturbed inner Appalachian belt of 

 upturned Pal&'ozoic rocks and the outer floor of gold-bearing Quebec Group (Primodial — 

 Potsdam S. S.) rocks, upon which the Middle Secondary and Cretaceous deposits were; 

 thrown down : — are among the questions to be solved by another generation of geologists. 

 But this much I feel sure of, that the old cataclysmic doctrines cannot be upheld in the 

 light of our present geological knowledge. Erosion by wind and rain, sunshine and frost, 

 slow chemical solution, and spring and fall freshets, has done the whole work. I have 

 long taught that it could not have been accomplished under water level by oceanic cur- 

 rents, because the ocean is a maker and not a destroyer. But I must now .abandon 

 wholly the idea to which I have clung, with a slowly relaxing grasp, so many years, that 

 a complete erosion theory demanded some such forces as would have been supplied by the 

 extra efficiency of an ocean translated across the upheaved surface through the air. At 

 the same time, the above considerations make me all the less willing to admit the ice- 

 cake theory of erosion as even approximately true. For if aerial erosion has been going 

 on uninterruptedly ever since the uprise of the Coal Measure continent, how little of 

 the whole (-fleet can have remained over to be still produced at the time when the Glacial 

 epoch set in and the supposed ice-cake began to take the work in hand. The battle has 



