GEOLOGY OF LAKE PLEASANT QUADRANGLE 59 



Beginning with the succeeding Trenton time our region, as well 

 as all the southern Adirondack area, subsided to allow an encroach- 

 ment of the Trenton sea in which were deposited first the Lower 

 Trenton limestone (very thin in the Lake Pleasant quadrangle) 

 and then the Canajoharie (Trenton) shale. During this time the 

 heart of the Adirondack area almost certainly was not submerged ^ 

 and it may be that this dry land area extended far enough south- 

 ward to include the northwestern corner of the Lake Pleasant quad- 

 rangle. At any rate the pebbles and sand grains already described 

 as occurring in the Trenton limestone near Wells prove comparative 

 nearness to a land area of Precambric rock while this Hmestone was 

 forming. 



There is no positive proof that any Paleozoic strata later than 

 the Canajoharie ever were deposited within the area of the quad- 

 rangle, though the next succeeding Schenectady shales quite likely 

 were. 



At some time during the middle or late Paleozoic era, there 

 occurred a great uplift (or uplifts) when the whole Adirondack 

 region, then largely mantled with sediments, was brought well 

 above sea level. This upward movement may have been inaugurated 

 at the time of the Taconic revolution at the close of the Ordovicic, 

 though it is generally thought that the major uplift occurred toward 

 the close of the Paleozoic era or at the time of the Appalachian 

 revolution. This upward movement in northern New York was 

 unaccompanied by folding, but there was a general down tilting 

 of the Paleozoic strata to the south or southwest. It is quite pos- 

 sible that some of the extensive faulting of the quadrangle accom- 

 panied the uplift either at the close of the Ordovicic or of the 

 Paleozoic or both. 



Mesozoic history 



As a result of the great upHft (or uplifts), another vast erosion 

 cycle was inaugurated and none of the southern Adirondack area 

 has ever again been covered by sea water. This erosion cycle con- 

 tinued till the close of the Cretacic period when the area of the 

 quadrangle was again reduced to the condition of a fairly good 

 peneplain and the Paleozoic strata were largely removed. No 

 very definite idea of the character of this peneplain within the 

 quadrangle can be gained because of subsequent movements and 

 erosion, but it is known to have extended over much, if not all, 

 of New York State, southern New England, and the Appalachian 



1 See evidence presented in the paper above cited. 



