58 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 76 



nearly 20 years ago in my " Revision of the Paleozoic System " -'^ 

 under the general designation of continental and local " tilting " 

 and " warping." Much was Imown even then about the north-south 

 and east-west tilting of the only slightly deformed interior area of 

 the continent, but we learn of new instances almost every year. We 

 knew something also of the similar movements in the Appalachian 

 region, but in this much less stable geosynclinal region the new ap- 

 plications of the theory have accumulated faster than we can ade- 

 quately assimilate and adapt them to the general scheme. A recently 

 published paper by Butts ^^ gives a fair but incomplete statement of 

 the present status of Appalachian Valley stratigraphy and of the 

 frequent warping and tilting and consequent shifting of land and 

 water areas to which this region was subjected during most of the 

 Paleozoic periods. 



Time required to effect observed modifications of faunas now avail- 

 able. — If my conception of the age relations of those formations 

 in the southern and northeastern thirds of the Appalachian geosyn- 

 cline and, on the other side of the Atlantic, in Scotland, Norway, 

 Sweden, and Bohemia that contain fossil remains of the Ordovician 

 middle Atlantic faunal realm is correct it obviously greatly expands 

 our previous estimate of the aggregate volume of the marine sedi- 

 ments of this period and also of the time required to deposit them. 

 However, even this expansion fails to cover all the missing links of 

 the whole span of time involved, for it does not take into account 

 the probable inaccessibly recorded but logically inferable intervals 

 between the alternating and very slowly effected north-south and 

 eiast-west tiltings during which the waters of the Atlantic were con- 

 fined to the oceanic basin between the continents. At those times the 

 continents were too completely emerged to permit marine deposition 

 in the surficial troughs and basins that at other times suffered 

 Atlantic invasion and sedimentation. Under my conception these ad- 

 ditional times are required to produce the structural modifications 

 that distinguish the successively evolved stages or "species" that 

 are preserved in the accessible stratigraphic record which, of course, 

 is everywhere more or less fragmentary. Natural evolution, as it 

 seems to me, was always an exceedingly slow process. Supposed or 

 suggested fossil instances of saltatory changes usually prove to have 

 been initiated long before. As a rule the production of the results 

 that are being gradually uncovered by paleontological investigations 

 required more and ever more time than was granted by preceding 

 interpreters of geologic history. Thanks to the physicists and 

 chemists all the time we may require seems now available. 



^ Gool. Soc. America Bull., vol. 22, p. 291-680, 1911. 



" Butts, Charles, Variations in Appalachian strati,Traphy, Wash. Acad. Sci. Journ., 

 vol. 18, No. 13, pp. 357-380. 



