GEOLOGY OF THE LONG LAKE QUADRANGLE 49T 



the Long Lake quadrangle constitutes the northern portion of 

 the first of these lowland belts. A similar, though less conspicuous 

 lowland belt is developed across the south center of the quad- 

 rangle, again located on the Grenville rocks, and separating the 

 two highland areas of the quadrangle. 



Peneplains. It has been elsewhere shown to be probable 

 that, during Mesozoic time, the Adirondack region was worn 

 down to a comparatively even surface or peneplain, which was 

 subsequently uplifted, and that the accordant levels of the hill 

 and ridge tops and crests observable in the southern and western 

 Adirondacks are due to the fact that they are remnants of this 

 old surface.^ The uplift renewed erosion and the present broad 

 valleys of the region were cut out, the comparatively concordant 

 levels of their bottoms marking the new base leA^el, and their 

 depth below the peneplain horizon measuring the amount of 

 uplift. Since their development there has been further uplift of 

 the region, the old valley bottom level is no longer the stream 

 grade, and the streams are now engaged in the task of cutting 

 down to the new grade, in which task they have made but slight 

 progress. 



All these uplifts have somewhat tilted the old peneplain sur- 

 face though the amount of tilting is but slight, and in the southern 

 and western regions the even sky line of the ridges is everywhere 

 notable. But on the northeast the ridge tops appear at varying 

 altitudes and hardly suggest a peneplain surface. This is thought 

 to be due to renewed faulting during the more recent times of 

 uplift, giving the various fault blocks differing altitudes, and 

 destroying their previous concordance of surface. It seems also 

 to be true that monadnocks, or parts of the old surface which 

 were never worn down to the general peneplain level, are larger 

 and more abundant in the vicinity of the main axis of elevation 

 than they are elsewhere, and this makes an additional obstacle 

 in the way of recognition of that surface. 



The probability that faulting has played some part in the 

 production of the present topography of the district, though b}^ 

 no means as important a part as it has farther eastward, has 

 already been indicated. Therefore more evidence of former pene- 

 plaination should be observable here than there. An inspection 



I N. Y. State Mus. Bui. 95, p. 423-27; Ogilvie, I. H. N. Y. State Mus. BtU. 96, 

 p. 468-69. 



