266 SMYTH — KOCKS OF NORTHWESTERN ADIRONDACK REGION. 



The marked resemblance of the limestone series to the Grenville series 

 of Canada has been noted by Van Hise.^ with the suggestion that they are 

 equivalent. The difficulty of establishing such equivalency leads the 

 writer to prefer a local designation for these rocks, and he has elsewhere t 

 suggested the term Oswegatchie series. 



Gneissic Areas. 



The areas intervening between the belts of limestone are occupied by 

 gneisses whose origin and relation to the limestone series constitute one 

 of the most important problems presented by this region. In many 

 cases the portions of these gneisses immediately adjacent to the lime- 

 stone closely resemble the interbedded garnetiferous gneisses and doubt- 

 less should be regarded as members of the limestone series. These va- 

 rieties usually pass somewhat gradually into more massive gneisses of 

 plutonic aspect, and cases are not few where the latter are in direct con- 

 tact with the limestones. It is difficult to resist the impression that 

 these massive gneisses are, at least in part, of igneous origin, and that 

 this is sometimes the case will be shown below, but whether or not it 

 may be accepted as a general explanation it is impossible to say at pres- 

 ent. To the writer it seems probable that absolute proof as to the origin 

 of many portions of the gneiss will never be found. 



Igneous Rocks. 



The rocks of undoubted igneous origin may be classed, with few ex- 

 ceptions, as granite, diorite, gabbro and diabase. Of these the first two 

 have been in part described by the writer in another paper,J so that a 

 brief summary of the facts then stated will suffice. 



Granite and Diorite. 



A more or less interrupted ridge of granite extends across the townships 

 of Antwerp, Rossie and Gouverneur, and has not been traced to a limit 

 on the east. Besides this, there are numerous isolated masses scattered 

 irregularly about. It is a biotite-granite or granitite, whose intrusive 

 nature is shown at many points where it breaks through the limestone. 

 The structure of these contacts admits of no doubt of their character, 

 but metamorphism, while not absent, is hardly as extensive as might 

 be expected. Diorite appears as a basic phase of this granite, with a 



■ * Bull. 86, U. S. Geological Survey, p. 508. 

 t Report to State Geologist of New York (unpublished). 

 X Trans. New York Acad. Sci., vol. xii, p. 203. 



