PRECAMBRIAN ROCKS 

 Grenville Series 



General statements. Scattered throughout the Adirondack 

 region there are many large and small areas of an exceedingly old 

 series of stratified rocks. They belong among the most ancient 

 known (Archeozoic) of all rocks of the earth. In fact no rocks 

 of any kind have ever been found to be older than this series of 

 strata to which the name " Grenville " has been applied because of 

 an early description of typical rocks of the series in a town of that 

 name in the St Lawrence Valley of Canada. These rocks have 

 been profoundly altered (metamorphosed) from their original con- 

 dition as limestones, sandstones and shales into crystalline or mar- 

 ble, quartzites, and schists or gneisses, but the old stratification sur- 

 faces are generally remarkably well preserved. 



In view of the facts that the Grenville strata are rather exten- 

 sively developed in the Adirondack region, especially in the adjoin- 

 ing North Creek quadrangle, and that only a few very scattering 

 observations had ever been made in the Luzerne quadrangle, it was 

 hoped that the latter quadrangle would show large areas of Gren- 

 ville which, after careful study, might throw further light upon this 

 rather remarkable series of rocks. In this regard, however, the 

 writer was disappointed because the masses of pure Grenville in the 

 Luzerne district are notably smaller and fewer in number than usual 

 in northern New York quadrangles. The combined areas of Gren- 

 ville in the Luzerne quadrangle, free enough from intimate asso- 

 ciation with igneous rocks to be separately mapped as such, amount 

 to less than 3 square miles. 



The very " patchy " distribution of the Grenville series through- 

 out the Adirondacks is due to the fact that the once universally 

 present body of strata was invaded, cut to pieces, and locally in- 

 jected by great volumes of molten rocks, mainly represented by the 

 present extensively developed syenite-granite series. In the areas 

 mapped as Grenville and gabbro or granite mixed rocks, much of 

 the old stratified series is represented though not in a pure condi- 

 tion. Important additional light upon the stratigraphy and thick- 

 ness of the Grenville series has not been forthcoming as a result 

 of the study of the Luzerne quadrangle. 



The Grenville strata were deposited under water which covered 

 many thousands of square miles of northern New York and eastern 



fii] 



