170 Prof. Dana — Mefa))iorp/iism of Massive Crystalline Rocks. 



ceous and gneissic, with some garnets, the bedding distinct, and 

 N. 27'^ W. in strike as at the east end. 



This ledge, although made up mainly of massive norite and augite- 

 norite, bears thus positive evidence of its having once had bedding 

 throughout, and affords thereby a demonstration that its norite is of 

 metamorphic origin, and that the associated beds comprised also the 

 limestone of the region. 



(5) A bed of quartzite in norite. — About half a mile east of the 

 limestone number 5, about the Montrose Station, the rock is the 

 ordinary dark-coloured norite. 120 yards up the road going north- 

 eastward from the station, a bed of whitish granitoid quartzite outcrops 

 on the roadside for seventy yards, first on the west and then on the 

 east side. This bed of quartzite overlies norite. The norite near the 

 quartzite is micaceous, quartzose and schistose, and that underneath 

 is of the ordinary massive kind. There is evidence also that the bed 

 of quartzite has norite above as well as below it. The quartzite 

 looks somewhat like a pale quartzose porphyritic granite ; but, as 

 observed in thin slices, the quartz consists of aggregated grains like 

 sandstone ; showing a resemblance to the Peekskill quartzite. The 

 felspar is mainly orthoolase. 



C. Conclusions as to the Coktland Eocks. 



Many more observed facts might be here reported. But the above 

 appear to be sufficient to settle the question as to the relations of the 

 rocks of the Cortland series. They appear to sustain fully the 

 following conclusions : — 



(1) These rocks, although they include soda-granite, norite, 

 augite-norite, diorite, hornblendite, pyroxenite, and chrysolitic 

 kinds, are not independent igneous rocks erupted from great depths. 



(2) However complete their former state of fusion or plasticity 

 may have in some cases been, they are metamorphic in origin. 



(3) The strata that underwent the metamorphism were one in 

 series and conforraability with the adjoining schists and limestone, 

 and were part of the Westchester limestone series. (They are younger 

 rocks if of diffei'ent age, since they contain and intersect portions of 

 the Verplanck limestone.) 



(4) These Cortland rocks differ from the other Westchester County 

 rocks because the metamorphic process had to do with sedimentary 

 beds that differed in constitution or were in some respects under 

 different conditions from those that existed elsewhere. 



On the view reached, it follows that the limestones, schists, and 

 other rocks of the Cortland region originally constituted together one 

 series of horizontal strata. They underwent an upturning through 

 subterranean movements, and in the course of it, they became 

 metamorphosed ; ])art into mica-schist and gneiss, part by loss of 

 bedding, into the massive rocks. The number of these rocks does 

 not imply widely different ingredients in the original strata. For 

 hornblendite and pyroxenite have the same chemical constitution ; 

 the chrysolitic rocks contain no ingredient not in them also, and are 

 peculiar mainly in their less proportion of silica. Moreover, the 



