MAJOR STRUCTURAL FEATURES 325 



MAJOR LIXEAR FOLDS 



As has been already stated, previous discussions of the Appalachians 

 have been confined to the closely folded belt; little was said of the gently 

 folded rocks except that the Appalachian folds die out northwestward; 

 only cursory mention has been given to the rocks underlying the Paleo- 

 zoic. In order to know the Appalachians in full, however, it is necessary 

 to consider all the territory from the Atlantic Coastal Plain to and even 

 beyond the Mississipjji. A brief presentation was made in 1914 l)y the 

 author of the results of such analysis for the folded belt and the older 

 rocks lying southeast of it. The results of a similar analysis, not only 

 of the folded rocks but of the gently flexed area of the Mississippi A^alley 

 and Great Lakes district, are presented herewith in plate 4. The syn- 

 clinal and anticlinal axes shown thereon are, of course, generalized and 

 locally compounded of a number of minor folds. The simple process was 

 followed of plotting on the map the highest part of each anticline and 

 the lowest part of each syncline, which was in fact the only thing to do. 

 In this work there were used an enormous number of maps and reports, 

 in the preparation of which most American geologists have had a hand 

 at some place. 



Some of the major structural features were described long ago, such, 

 for instance, as the Cincinnati arch, Xashville dome, the Ozark uplift, 

 the Wisconsin dome, the West Virginia coal basin, and the Michigan and 

 Illinois coal basins. The Cincinnati arch has: been assigned a variety of 

 directions, usually trending between the east and southeast. This states 

 part of the truth, but omits the intersecting anticline which parallels the 

 Appalachian folds. This connects the Xashville dome in Tennessee with 

 the Cincinnati arch, separates the Appalachian coal basin from that of 

 western Kentucky and Illinois, separates the Michigan from the Appa- 

 lachian coal basin, and thence runs northward into the Ontario projec- 

 tion of the Precambrian of the Canadian shield. The Appalachian coal 

 basin is well known from Alabama to New York and often described. 

 The northern extension of the fold through New York is equally clear, 

 and it parallels with great closeness the anticline of the Blue Eidge and 

 Green Mountains, which is the chief anticline of the Appalachians. It 

 also parallels the major anticline of the closely folded belt west of the 

 Blue Eidge. This great anticline formed one element of the Adirondack 

 dome and raised a belt of Cambrian across the Saint Lawrence Valley. 

 Southward it brought the Adirondacks close to the Catskills and has 

 shown an excess of uplift through most of the Paleozoic. It is traceable 

 always as a major fold practically to the end of the Appalachians in 



