10 



NEW YORK STATE MUSEUM 



They have recently been found in the adjoining Little Falls dis- 

 trict. 1 Cushing notes the presence of limestone boulders near the 

 northern edge of the Little Falls sheet which makes it probable 

 that the limestone occurs on the Wilmurt sheet which lies east of 

 the Remsen sheet. Another occurrence is at Fourth lake of the 

 Fulton chain. 2 Thus it appears that the Grenville limestones are 

 only poorly developed along the southwestern border of the Adiron- 

 dacks. 



The strongest evidence for the original sedimentary character 

 of the Grenville rocks within the Remsen quadrangle is the fact 

 that layers of very different composition and color are in sharp 

 contact and often show rapid alternations. Such phenomena are 

 well exhibited in the Black river gorge at Enos, where the rock 

 layers stand in almost vertical position and strike n. 70 e. Near 

 the old mill there are many layers of very light color made up 

 almost entirely of feldspar and quartz. These rocks must orig- 

 inally have been beds of feldspathic sandstone and it appears 

 probable that the present banding corresponds closely to the 

 former stratification of the sandstone. These light colored layers 

 are clearly interbedded with dark gray and almost black feld- 

 spathic and hornblendic or biotitic rocks. Although some of 

 these darker rocks appear to be of igneous origin and closely asso- 

 ciated with the Grenville, nevertheless many of them are more 

 than likely of sedimentary origin and were probably originally 

 shales. 



Another strong evidence for the sedimentary origin of the Gren- 

 ville rocks is the presence of graphite in them. Graphite flakes 

 often a millimeter or more across and exhibiting a shiny metallic 

 luster are very common in certain of the lighter gray layers near 

 the mill' at Enos. More rarely the graphite occurs in the darker 

 layers. It is difficult to account for the graphite except on the 

 basis of organic origin. Thus we may argue that the original 

 sandstones and shales were more or less carbonaceous and during 

 the process of metamorphism the organic matter was changed and 

 crystallized into graphite. 



Another mineral suggesting a sedimentary origin which is often 

 found in light red crystals, especially in the darker layers, is garnet. 

 Garnets are rather more frequently present in metamorphic rocks 

 of sedimentary origin and their presence here, often in abundance, 

 seems to suggest such an origin for the Grenville. 



1 Professor Cushing has called the writer's attention to the discovery of this limestone 

 by D. H. Newland. See N. Y. State Mus. Bui. 119. p. 143. 



2 Smyth, C. H. jr. Crystalline Rocks of the Western Adirondacks. N. Y.- State Mus. 

 51st An. Rep't, v. 2. 1897. 



