36 NEW YORK STATE MUSEUM 



Contact phenomena 



A very interesting case of contact metamorphism produced by 

 the action of the gabbro on granite may be seen at the southern 

 end of the large stock just south of Mountain Spring lake. In a 

 recently opened stone quarry, and about 75 feet higher than the road 

 on its east side, the rocks are laid bare in such a manner that an 

 excellent opportunity is afforded for the study of the contact zones. 

 The following nine zones, passing from the typical gabbro to the 

 typical granite (country rock), have been studied in detail in the 

 field and by means of thin sections and hand specimens. 



Zone I Typical gabbro well within the gabbro stock. Nearly black, 

 medium grained, and with diabasic texture. (Gradation 

 from I to 2) 



Zone 2 Syenitic phase of gabbro stock and within a few feet of the 

 granite. Dark gray, medium grained, and with granitoid 

 texture. (Gradation from 2 to 3) 



Zone 3 One to three feet wide. Biotite-schist, border phase of the 

 gabbro stock. Secondary origin. (Sharp contact between 

 3 and 4, gabbro and granite) 



Zone 4 Four inches wide. Hornblendite phase of the country rock. 



Nearly black,, medium grained, banded parallel to gabbro- 



' granite contact. (Fairly sharp contact between 4 and 5) 



Zone 5 Six inches wide. Monzonitic phase of the country rock. 

 Yellowish gray, medium to coarse grained, and banded 

 parallel to the main contact. (Not very sharp contact 

 between 5 and 6) 



Zone 6 Fifteen to eighteen inches wide. Chiefly hornblendite phase 

 of the country rock but with numerous very narrow 

 streaks of no. 5. Nearly black, medium grained, and 

 banded parallel to the main contact. (Sharp contact be- 

 tween 6 and 7) 



Zone 7 Three and one-third feet wide. Monzonitic phase of the 

 country rock like no. 5. Yellowish gray, fairly coarse 

 grained, and banded parallel to the main contact. ( Not 

 very sharp contact between 7 and 8) 



Zone 8 Seven feet wide. Monzonitic phase of the country rock. 

 Light gray, fairly coarse grained, and not l)anded. (Gra- 

 dation from 8 to 9) 



Zone 9 Typical (country rock) granite. Pink, medium grained, and 

 very gneissoid but with gneissic batlds striking at almost 

 right angles to the main contact. 



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