326 A. KEITH OUTLINES OF APPALACHIAN STRUCTURE 



Alabama. The anticline which passes through the Ozark and AVisconsin 

 domes almost severs the Illinois coal basin from the great basin of Iowa, 

 Missouri, and Kansas. 



CROSS-STRUCTURES 



The structures heretofore considered are those which run for great 

 distances parallel to the trend of the range and which are so strongly 

 dominant that they have received practically all of the attention given 

 to Appalachian structure. These by no means, however, include all of 

 the Appalachian structures. Folds rise and pitch along their axes, form- 

 ing saddles and peaks; they curve and they die down. Such structures 

 were well brought out by the early surveys of Pennsylvania and Virginia, 

 where the phenomena are most striking. These were regarded as purely 

 local, however, and no special significance was attached to them. No 

 attention seems to have been paid to the numerous diversions from 

 the normal structural trend. Some years ago the author read a paper 

 before the Philosophical Society of ATashington which showed by dia- 

 grams that there was a system in these structures and that there were 

 certain lines across the general trend on which anticlines tended to be 

 higher or synclines lower. These were called cross-folds. Certain other 

 lines or narrow zones called cross-warps were characterized by the swerv- 

 ing of many axial lines out of the normal in the santie direction. The 

 author was advised not to publish this, however, because it seemed too 

 revolutionary. At later dates, in various folios of the United States 

 Geological Survey, the author has described instances of these structures, 

 and a general affirmation of them as a system was made in 1914 in the 

 writer's presidential address to the Geological Society of Washington. 



These cross-warps are exhibited on a very large scale, and in this dis- 

 cussion are called salients and recesses. Cross-warps on a much smaller 

 scale are numerous and decided. A particular striking one crosses East 

 Tennessee just north of Ejioxville and passes into North Carolina. Its 

 effects are plainly visible in all of the rocks from Kentucky into North 

 Carolina, including the gently folded strata of the coal basin, the highly 

 tilted beds of the Ordovician and Cambrian of the Appalachian Valley 

 and Mountains, and the schists and gneisses of the Precambrian. This 

 local cross-warp springs from the North Carolina salient and is associated 

 with a great block of the earth's crust, TO miles long, which has been 

 visibly thrust northwest 8 or 10 miles on the Pine Mountain fault of 

 Kentucky and Tennessee. This fault has the usual northeast trend ex- 

 cept at its ends, where it swerves abruptly to the southeast. The south- 

 western swerve was mapped and described in the author's Briceville folio. 



