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to be such. This is the only occurrence yet noted which may 

 possibly invalidate the preceding statement. At the best this is 

 only negative evidence, but it is desired to call attention to the 

 possible light which these dikes may shed on the age of the 

 gneisses. 



Grenville series 



Rocks which can be referred with certainty to the Grenville 

 series are but sparingly shown in Franklin county, and occur in 

 small disconnected patches instead of considerable belts. 1 But 

 eight areas of sufficient size to appear on a small scale map have 

 Tjeen noted, and of these six occur surrounded by rocks which are 

 unquestionably igneous, and are not only of later date than the 

 Grenville rocks but probably of later date than those gneisses 

 whose origin is questionable. Inspection of the map shows that 

 six of these eight patches have such position with respect to one 

 ^another, that they seem to represent remnants of what were origin- 

 ally two continuous and parallel northeast and southwest belts, 

 such as are now found in St Lawrence county infolded with other 

 gneisses. Here in Franklin they have been invaded by great 

 igneous intrusions, and all save these mere patches have disap- 

 peared. The contrasting conditions in the two counties can 

 <juite plausibly be explained by supposing that a greater erosion 

 lias taken place in Franklin county, so that rocks originally more 

 deeply buried are now exposed at the surface there, whence it 

 would follow that similar conditions now exist in St Lawrence at 

 ^ome distance below the surface. It should be said also that the 

 fact of greater erosion in Franklin county is supported by inde- 

 pendent evidence, instead of being a mere supposition brought 

 forward for the purposes of this explanation. 



Rocks of the Grenville series. The most striking and character- 

 istic rocks of the Grenville series are the limestones. These are 

 coarsely crystalline marbles which contain, even when purest, 

 scales of graphite and phlogopite and grains of green pyroxene, 

 -and often apatite and titanite as well. Some very pure-looking 

 toeds prove to be composed of nearly equal parts of calcite and 



lSee map accompanying this report. 



