Buckley — Ice Ramparts. 159 



regarded as dipping toward the force." ^ Such folds are over- 

 thrust folds. The reason that overthrust rather than under- 

 thrust folds commonly form is that the direction of easiest relief 

 is upward rather than downward.^ That is the manner in 

 which the forces have acted, as sho^\ai hy Dr. Buckley, in the 

 case of a majority of the overturned folds described by him. 

 He observes in reference to the folds along the shore that 

 ^Vherever the folds were near a high shore line they were al- 

 most invariablv overthrust.'^ 



Another point of great interest is the successive development 

 of folds formed along marshy shores. I have explained that 

 parallel folds in the earth's crust are probably successive. As a 

 result of the formation of the first fold the strata are piled up 

 and thickened. ''After a time the increased thickness of ma- 

 terial is sufficient to present a larger total resistance to deforma- 

 tion than the thinner strata in advance. The stress will then 

 be transmitted forward. On account of the greater stress per 

 unit of area, a second fold similar to the first will then be 

 form.ed, but this results in again thickening the mass subject to 

 the force couple, and again the stress is transmitted forward. 

 A new inclined fold is then produced, and so on.''^ While par- 

 allel folds are largely successive, one fold does not completely 

 develop before the next begins to form. This sequence inferred 

 for mountains a number of years ago is exactly paralleled by 

 the manner in which the folds formed in the soft marsh as de- 

 scribed by Dr. Buckley. 



Dr. Bucklev observed that in the successive ice and marsh 

 folds the anticlines are elevated much more than the synclines 

 are depressed. This upon theoretical grounds I have held to be 

 a general truth for the anticlines and sjaiclines of mountain 

 masses. * 



Another very interesting thing in reference to the formation 

 of the ice and swamp folds is that where two sets form they are 

 at right angles to each other. (See p. 146.) This same phe- 

 nomenon is very characteristic of crustal folds, and the explana- 



1 Principles of North American Pre-Cambrian Geology, by C R. Van Hise ; 16th Ann. 

 Rep., U. S. Geol. Surv., Pt. I, 1896, p. 621. 



' Principles cit., p. 622. 



' Principles cit., p. 622. 



* Estimates and Causes of Crustal Shortening, by C. R. Van Hise : Journ, of Geol., Vol 

 6, 1898, p. 19. 



