W J MCGEE THE APPOMATTOX FORMATION. 540 



name has hitherto been proposed. The class, too, is more comprehensive than Pro- 

 fessor Davis' question might indicate. In the Buhrstone hill-land a well-defined drain- 

 age was established in late Eocene time; and rivers, streams, brooks, rivulets, down 

 to the minutest rills even, and a corresponding topographic system, were developed. 

 Subsequently the Grand Gulf formation of the Miocene was laid down and the old 

 surface was buried in part, yet not so completely buried but that the post-Miocene 

 drainage coincided with the pre-Miocene drainage. Then came the Appomattox for- 

 mation, which was spread like a mantle over the surface; and upon it the primary 

 drainage was once more renewed. Afterward the Pleistocene Columbia formation 

 was laid down ; and then for the fourth time was the drainage outlined on the original 

 lines. This class of drainage has not hitherto received a designation ; but from its 

 mode of origin it might be called resurrected, or palingenetic. 



Mr. C. D. Walcott : I have listened with a great deal of interest to Mr. McGee's 

 paper, because it describes the determination of a geologic horizon over a great area 

 without the aid of paleontologic data. It is true that the underlying unconformable 

 series is determined by the contained fauna and gives the approximate horizon, but it 

 is very rarely that we have an illustration of a satisfactory attempt to identify by the 

 stratigraphy alone a formation so widely distributed as the Appomattox. 



Professor James Hall : The communication shows very clearly that physical geol- 

 ogy can be successfully carried on without the use of fossils. 



The next paper was — 



THE VALUE OF THE TERM "HUDSON RIVER GROUP " IN GEOLOGIC 



NOMENCLATURE. 



BY C. D. WALCOTT. 



It was discussed by James Hall, W. M. Davis, and Mr. Walcott. The 

 paper and discussion are published in full among the memoirs, pages 335- 

 .356 of this volume. 



The following papers were then read : 



THE CALCIFEROUS FORMATION IN THE CHAMPLAIN VALLEY. 



BY EZRA BRAINERI) AND II. M. SEELY. 



THE FORT CASSIN ROCKS AND THEIR FAUNA. 



BY R. I\ WniTFIELT). 



Both of these communications are printed in full among the memoirs, 

 orming the preceding pages 501-516. 



The Society then adjourned until 10 a. m. of the next morning 



LXXiri— Rum Geol. Soc. Am., Vol. 1, 1889. 



