AMERICAN GEOLOGY EATONIAN ERA, 1820-1829. 



277 



year, is figured and described what is evidently an overturned fold. 

 This is of interest, since while the nafure of the fold was partially 



realized, the means by which it was brought about was 

 Overturned Folds, considered as problematical. Similar phenomena had 



been noted by Eaton (p. 253) and by Maclure, but with 

 nothing like as much detail. The writer says: 



It is impossible to examine this locality without being strongly impressed with the 

 belief that the position which the strata here assume could not have been effected 

 in any other way than by a power operating from beneath upward and at the same 

 time possessing a progressive force, something analogous to what takes place in the 

 breaking up of the ice of large rivers. 



The continued swelling of the stream ^^ L — .__^ £=? . ^^ 



first overcomes the resistance of its ==_ 



frozen surface, and having elevated ^=^' _ _§?~ = 



it to a certain extent, it is forced .--^r^^^ ~K= ""■ .-.. 



into a vertical position, or thrown -— — =^~ " 



over upon the unbroken stratum be- 

 hind, by the progressive power of the 

 current. 



If it can be admitted that the oper- 

 ation of such a power did produce the 

 effect here represented, it must have 

 taken place before the materials of 

 which the formation is composed had 

 passed into an indurated state, as 

 most of the strata remain unbroken, 

 and, where the argillite has crum- 

 bled away, the curved part of the 

 graywacke may be taken oat entire, 

 and some of them, which I now have 

 in my possession, exhibit indenta- 

 tions and protuberances, particularly 

 on their curved surfaces, evidently 

 the result of friction while in a plas- 

 tic state. 



Fig. 17.— Sections of Snake Hill, Saratoga Lake. 

 (After J. H. Steel.) 



The description is of still fur- 

 ther interest historically, when 

 considered in connection with 



the dispute relating- to priority of discovery which later arose between 

 Messrs. Hitchcock and Rogers. (See p. 31l.) 



The fact that rock strata were not always found lying even approx- 

 imate^ horizontal had been often noted, but no rational explanation 

 suggested or, indeed, attempted. In that year, however, Maclure, in 

 noting the fact that the Transition rocks dip, suo-p-ested 



Inclined Strata and ° . l ' tete 



the possibility of its being caused by their having 

 been "disposed on the primitive, concerning which 

 we can as yet scarce conjecture anything." 



Overturned Folds 



1825 



