22, NEW YORK STATE MUSEUM 



The Precambric rocks are classifiable in order of age from the 

 latest to the oldest as follows: 



The unmctamorphosid basalt ic dikes 



Tiie erupik'c complex of more or less metamorphosed granites. 

 anorthositcs, syenites, gabbros and intermediate types. 



The GrenviUe series of limestones^ ophicaicites, schists, and sedi- 

 mentary gneisses 



Granville series. Ti:e name Gren\Tlie was originally given by 

 Logan to a series of rocks in all respects similar to tlie one here 

 under discussion and developed in the township of Gren\-ilie, On- 

 tarij. Ebenezer Emmons in his earl}^ work in the Adirondack area 

 spoke of them as primary, a3id, under this head, placed the lime- 

 stones (called primitive limestone) and the serpentine with the ig- 

 neous rocks, while the gneiss was classed with the stratified. It \t 

 one of the curious instances of the changes in geological thought. 

 that 60 years later these views are exactly transposed. In later 

 years the wise custom has developed of applring geographical 

 names to formations and for tliis reason the term Grenrille is here 

 adopted. It is true that a gap intervenes betAveen the Adirondack? 

 and the Canadian exposures in Quebec and Ontario, and that this 

 gap is covered by the Paleozoics. but the similarit}^ of the old sedi- 

 ments in both areas is so great, that there seems little doubt that 

 they are equivalcnls. The International committee, wliich risite i 

 l>oth regions in 1906 and submitted a report on the correlation of the 

 two were at least sufficiently impressed with the similarity to 

 leccnimend tlie uniform use of Grenrille.^ 



The Grenville strata are widespread in tlie Adirondacks, scarcel}^ 

 a quadrangle being without them. On the Port Henr\- sheet and 

 along Lake Champlain just north of Port Henr\^ is one of the best 

 exposures in the eastern mountains, but they also appear at a 

 number of other localities in the area here described. 



The most prominent and easily recognized of tj:ie members is a 

 white cr\-stalline limestone. ver>^ coarse grained and seldom pure 

 or uniform over any great width. It is marked by small inclusions 

 of pyroxene, graphite and less common indiridual minerals and 

 by larger streaks and pegmatitic aggregates of coarse quartz, feld- 

 spar, hornblende, biotite, tourmalin, titanite. pxirhotite and scapo- 

 lite. AMiere the limestone has been quarried for fluxing purposes 

 in the iron furnaces, as has been the case near Port Henr>\ large 

 dump= -f the rejected silicates have acctunulated, and now afford 



3Jciir. Gcol. 1907. 15:191. 



