ELIZAUETHTOWN AND FORT HENRY QUADRANGLES 1 7 



country into these marked divisions, and which by sheeting the 

 rock along the lines of movement has produced the vulnerable por- 

 tions, searched out by the moving water. Aside from the evidence 

 of the topography the inference is corroborated by the exposures 

 afforded in these and neighboring quadrangles by the waterfalls of 

 which there are a few. Thus at Split Rock falls in the Boquet 

 river about 7 miles southwest of Elizabethtown, the old crystallines 

 are sheeted and crushed in a most significant manner. Precipitous 

 escarpments display the same characteristics and yield often great 

 talus slopes of angular blocks with parallel sides. The localized 

 and close set grouping of the planes of separation irresistibly sug- 

 gests to the observer a fault line or zone rather than the simple 

 record of joints which of themselves are not easy to understand 

 except as composite faults of slight individual displacement. 



Of the geological date of this fault system it is difficult to form 

 an estimate. The youngest rocks aft'ected are Cambric and 

 Ordovicic. The freshness of the relief would suggest a time 

 possibly in the Tertiary, but undoubtedly the plucking of the Con- 

 tinental ice sheet and of local glaciation freshened up the relief 

 very greatly, by the production of bergschrunds.^ 



In the Paradox Lake quadrangle just south, Dr I. H. Cgilvie- 

 has detected flat-topped mountains which strongly suggest remnants 

 of an old peneplain, now broken into blocks by faulting. If this 

 peneplain marks the completion of the Cretaceous cycle of drainage 

 as is not improbable, the _ faults would be of Tertiary date. The 

 suggestion is however but a surmise and, as is always the case with 

 faults in the ancient crystalline rocks, the evidence is less easy of 

 attainment than in the stratified rocks with their contrasted beds 

 and fossils. 



Besides the northeast and southwest systems of drainage just 

 described there is in this quadrangle and still more in neighboring 

 ones evidence of north and south valleys, and of east and west 

 ones which are older. The latter are broader and more open ; their 



1 Bergscbrund is the word current in Switzerland for the space or 

 chasm which customarily intervenes between a glacier and the rocky 

 walls of the valley through which it moves. It is a place of specially 

 active removal of rocks because in the warmer seasons the ice melts 

 by daj^ from the sun and the water freezes again at night from the 

 cold. Glaciers thus gradually widen their valle\-s and render the sides 

 very steep. There seems to be no gnod English equivalent for bergscbrund 

 — therefore it is adopted as above. 



2 Geology of the Paradox Lake Quadrangle. N. Y. State Mus. Bui. 96. 

 1905. p. 468. 



