THE ADIRONDACK MOUNTAINS 3I 



PHYSICAL HISTORY OF THE ADIRONDACKS 

 Prepaleozoic History 



The most ancient (Grenville) rocks and history. The Adiron- 

 dack mountains are made up ahnost entirely of exceedingly old 

 rocks. Of these the most ancient known are called the Grenville 

 series, so named from a Canadian town in the St Lawrence valley. 

 Not only are the very earliest known records of the history of 

 northern New York written in these Grenville rocks, but also they 

 are to be classed with the very oldest recognized rock formations 

 of the earth. Only during the past 25 years has the real significance 

 of the Grenville and closely associated rocks in the Adirondacks 

 been discovered. 



The Grenville consists of a great series of sediments — original 

 muds, sands and limes — which were deposited layer upon layer 

 under water. The widespread extent of the series, far beyond the 

 limits of the Adirondacks, and their great thickness make it certain 

 that the Grenville sediments were accumulated on the bottom of a 

 relatively shallow ocean very much as sediments are now piling up 

 on the marginal sea bottom. Thus, the most ancient known geo- 

 graphic condition of the Adirondack district was an expanse of sea 

 water covering the whole area. 



It may occur to the reader to ask : How long ago did the Gren- 

 ville ocean exist? There are grave difficulties in the way of answer- 

 ing this question in terms of years since we have nothing like an 

 exact standard for such a measurement or comparison. Although 

 we must concede that not even approximate figures can be given, 

 nevertheless it can be demonstrated by several independent lines of 

 reasoning that the time must be measured by at least some tens of 

 millions of years, very conservative estimates ranging from 25 to 

 50 million years. In any case, the time is utterly inconceivable to 

 us, the important thing to bear in mind being that the great well- 

 known events of earth history which have transpired since the 

 existence of the Grenville ocean require a lapse of many millions of 

 vears as shown by the enormous accumulations of sediment in many 

 parts of the earth and the repeated revolutionary changes in geo- 

 graphic and geologic conditions. The ideas here expressed will be 

 much better appreciated by the reader after following through the 

 story of the Adirondacks as set forth in the succeeding pages. By 

 so doing, it is hoped that the reader will not only learn the main 



