PALEOZOIC TIME — CARBONIC. 729 



MOUNTAIN-MAKING IN NORTH AMERICA. 



The various steps in the making of the Appalachian Mountain Range, 

 or Synclinorium, and the events of the prolonged, catastrophe, have been 

 reviewed at length on pages 353-357. It is there stated that general quiet 

 prevailed over the continent throughout the Paleozoic eras, with the exception 

 of the interval of Taconic upturning, and those gentle oscillations of level 

 in the earth's crust that seem to have been always in progress. The extent 

 and steps of progress in the geanticline of deposition, which began in the 

 early Cambrian, has also been explained, and particulars mentioned as to its 

 variations in eastern and western limits, as shown by the limits of the several 

 formations ; and its inequalities in rate of subsidence over its different parts 

 and in successive periods, as indicated (1) by the varying thickness of the 

 formations from nothing to thousands of feet, and also (2) in the varying 

 kinds of rocks from shales to conglomerates and limestones. 



The review of the facts relating to the history of the successive formations 

 from the Cambrian onward has given greater definiteness and reality to the 

 events. Moreover, it has derived new illustrations of the changes from the 

 remains which the rocks contain of the life of the world. The varying con- 

 ditions of the preparatory geosyncline during its progress have thus become 

 strongly apparent ; and they will be much more so when the limits of the 

 successive formations, now so well understood over New York, shall have 

 been as thoroughly investigated by the paleontologist and geologist over 

 Pennsylvania, the Virginias, and beyond. 



The general facts connected with the upturning of strata, 30,000 to 40,000 

 feet thick, which the geosyncline at the end contained, have also been 

 reviewed ; and an account given of the flexures of the beds in many long lines, 

 and the general parallelism of the flexures, but with interruptions and over- 

 lappings, and of upthrust faults of 10,000 feet and more. Mention has also 

 been made of curves in the course of the finished mountain range ; one bending 

 from north-by-east in the northern or Catskill portion to east-northeast in 

 Pennsylvania, the whole nearly parallel with the eastern and southern outline 

 of the nucleal Archaean mass ; the other, from Pennsylvania to Alabama and 

 Mississippi, and becoming at the south nearly parallel with the Mexican Gulf. 



The courses and character of the flexures in the nearly east-and-west 

 portion of the range in Pennsylvania are well shown on Lesley's topographic 

 map of the state, although greatly disguised in consequence of the denudation 

 that has taken place since the time of mountain-making. A copy of the 

 map (Fig. 1153) is here introduced, exhibiting the courses of the multitudes 

 of ridges, and their bends and terminations either side of the channel of the 

 Susquehanna River. The map is here reduced to too small a scale to show 

 all the minor flexures, and a diagram is added (Fig. 1154) giving in simple 

 lines the courses, positions, and bends of the various ridges over the center of 

 the state. 



