INTRODUCTION. 253 



(c) The Trenton series is believed by Mr. Glenn to be included in the 

 higher Silurian outcrops. 



4. That no rocks of Upper Silurian age have yet been reported from the 

 area. 



5. That Shumard(?)* and Glenn f have reported the occurrence of De- 

 vonian rocks in the northeastern portion of the district, but that all other au- 

 thorities have believed them absent. 



6. That Hill has several times asserted that the Cretaceous beds once cov- 

 ered the whole of the Central Paleozoic region, and that he believed that the 

 latter are only visible now through erosion. 



7. That granitic intrusions or extrusions are supposed to have occurred at 

 different ages within the area, but that authorities differ widely in fixing the 

 chronologic order and positions of such disturbances. 



(a) The idea obtained from reading the opinions of all writers is that there 

 were only one or two epochs of disturbance; but 



(b) These epochs have been variously put at, (1) Pre-Cambrian (Walcott); 

 (2) Paleozoic (Shumard and others); (3) Late or even Post-Carboniferous 

 (Hill). 



(c) No one has assumed that, as is really the case, more than two uplifts 

 have occurred. 



The field work of 1889 is capable of much further amplification than will 

 be found in this report, but additional data must be obtained before it will 

 be safe to announce conclusions which may be yet in doubt for lack of the 

 most complete evidence. What is to be stated herein will therefore comprise 

 only those definite results which the facts known are believed to fully war- 

 rant. It may be well to state at this point that while certain of the items 

 quoted above have been verified by the writer's observations, as many more 

 have been found incorrect, and a very considerable amount of new and 

 wholly unexpected structure has been worked out. 



* Upon the doubtful authority of Buckley, as already quoted. 



f Manuscript (unpublished) report as State Geologist, 1874, previously noted. 



