320 National GeograjpTiic Magazine. 



topographic development, and finally flowing across the coal- 

 measure lowlands of recent appearance. It was across the lower 

 courses of such rivers that the Appalachian folds were formed, 

 and the first step in our problem consists in deciding if possible 

 whether the streams held their courses after the antecedent fash- 

 ion, or whether they were thrown into new courses by the grow- 

 ing folds, so that a new drainage systen would be formed. Possi- 

 bly both conditions prevailed ; the larger streams holding their 

 courses little disturbed, and the smaller ones disappearing, to be 

 replaced by others as the slopes of the growing surface should 

 demand. It is not easy to make choice in this matter. To de- 

 cide that the larger streams persisted and are still to be seen in 

 the greater rivers of to-day, only reversed in direction of flow, 

 is certainly a simple method of treating the problem, but unless 

 some independent reasons are found for this choice, it savors of 

 assumption. Moreover, it is diflicult to believe that any streams, 

 even if antecedent and more or less persistent for a time during 

 the mountain growth, could preserve till now their pre-Appa- 

 lachain courses through all the varying conditions presented by 

 the alternations of hard and soft rocks through which they have 

 had to cut, and at all the different altitudes above baselevel in 

 which they have stood. A better means of deciding the question 

 will be to admit pi'ovisionally the occurrence of a completely 

 original system of consequent drainage, located in perfect accord 

 with the slopes of the growing mountains ; to study out the 

 changes of stream-courses that' would result from later disturb- 

 ances and from the mutual adjustments of the several members 

 of such a system in the different cycles of its history ; and finally 

 to compare the courses thus deduced with those now seen. If 

 there be no accord, either the method is wrong or the streams are 

 not consequent but of some other origin, such as antecedent ; if 

 the accord between deduction and fact be well marked, varying 

 only where no definite location can be given to the deduced 

 streams, but agreeing where they 'can be located more precisely, 

 then it seems to me that the best conclusion is distinctly in favor 

 of the correctness of the deductions. For it is not likely, even 

 if it be possible, that antecedent streams should have accident- 

 ally taken, before the mountains were formed, just such locations 

 as would have resulted from the subsequent growth of the moun- 

 tains and from the complex changes in the initial river courses 

 due to later adjustments. I shall therefore follow the deductive 



