INTRODUCTION 311 



Systematic, detailed work was begun for the United States Geological 

 Survey in 1885 by Pumpelh^, Russell, Willis, Darton, Dale, and Hobbs; 

 in 1887 by Hayes and Keith; and in 1889 by Campbell; and it has been 

 carried on since that time by the Survey and by many individuals. In 

 recent years many of the State surveys have done their shares of the de- 

 tailed work. The present author has continued his work in the Appa- 

 lachians each year since 1887, though with many interruptions of late, 

 the first 20 years in the south, and in later years mainly in the north. 



In the following discussion the attempt will not be made to present 

 details, but only to state the general features and typical groups of facts 

 which have controlled the local facies of the deformation. Xext will be 

 given the generalizations of the phenomena according to time and space. 

 Following these, inferences will be drawn as to the direction, application, 

 and method of transmission of the deforming forces. This will be fol- 

 lowed by a brief statement of various theories of mountain structure and 

 their application to the Appalachians. Finally, a theory will be pre- 

 sented as to the immediate nature of the deforming force and as to its 

 ultimate source. The substance of the generalizations as to the strong 

 deformation of the Appalachians and its cause was presented by the 

 author in 1911 in his presidential address to the Geological Society of 

 Washington. In the present discussion the surroundings of the folded 

 belt are also analyzed, and the cause of the folding is more definitely 

 set forth. 



Definition 



The Appalachian folded belt is continuous from central Alabama to 

 New Brunswick, in Canada, a distance of 1,500 miles. Its southern ex- 

 tension is covered by the Cretaceous and Tertiary deposits along the 

 Gulf of Mexico, while at the north it passes beneath the Gulf of Saint 

 Lawrence and crosses the island of Newfoundland, making a total length 

 for the system in North America of 2,000 miles. If the general line of 

 the Appalachians is extended across the North Atlantic it crosses the 

 southern portions of the British Isles and thence passes into central 

 Europe. It thus appears to be part of a great system of folding called 

 the Armorican system by Suess, which has the same features and the 

 same age as the Appalachian system. The extension of the Appalachians 

 soutnwest of Alabama is problematical. Some geologists consider the 

 Ouachita Mountains of Arkansas and Oklahoma to be the western exten- 

 sion of the Appalachians, in which case the latter would be bent nearly 

 at a right angle. It seems to the author, however, that the Ouachita 

 folds, while developed at the same time, rose on one of the cross-axes 



XXI — Bull. Geol. Soc. A.m., Vol. 34, 1922 



