b 



GEOLOGY OF THE NORTH CREEK QUADRANGLE TI 



pyrrhotite scattered through the mass. The quartz grains usually 

 range in size up to five or six millimeters and stand out as pale 

 straw yellow or clear masses in very bold relief upon the weath- 

 ered surfaces. Tiny garnet and green pyroxene crystals are rarely 

 present. This variety is also widely distributed and among many 

 other good outcrops are: just east of North Creek; at the Natural 

 Bridge; just south of Crane mountain; and 1^2 miles due north of 

 Warrensburg. 



A third variety which is rather widely distributed though not 

 so common as those above described may be called serpentine lime- 

 stone or green marble. One kind of this rock is medium-grained, 

 nearly white, crystalline limestone but with many large blotches 

 or irregular streaks of dark to light olive green serpentine scattered 

 through it. A second kind has scattered through it numerous 

 specks of serpentine or small pale green serpentinized pyroxenes. 

 Different names have been applied to this green marble which has 

 been briefly described by G. P. Merrill who says ^ : " The serpen- 

 tine in the W^arren county Ophiolite, Ophicalcite or \'erdantique 

 as it has l^een variously called, is an alteration or metasomatic 

 product after a mineral of the pyroxene group. The original rock 

 would appear to have been simply a pyroxenic limestone, the py- 

 roxene occurring either in scattering granules or in granular aggre- 

 gates of considerable size." Among other places this green marble 

 is well shown in the quarries one-half of a mile southwest and 

 tliree-fourths of a mile southeast of Thurman village, and in the 

 prospect hole at the western base of Hackensack mountain. 



Pure white tremolite crystals are sometimes closely associated 

 with the limestone as in many outcrops about a mile east of Little 

 mountain pond. One and. one-half miles due north of Warrens- 

 burg irregular streaks or veins of tremolite, quartz, pyroxene, and 

 titanite are closely involved with the limestone. The tremolite 

 crystals are up to two inches long and the green pyroxenes up to 

 one-quarter of an inch and perfectly formed. 



Asbestos veins sometimes occur in the serpentine marble, these 

 being best shown at the asbestos mine three-quarters of a mile 

 southeast of Thurman where numerous veins attain a widtli up to 

 three-quarters of an inch. 



Green pyroxene or rusty biotite gneisses are sometimes involved 

 in the contorted limestone in the form of streaks or inclusions 

 which have been drawn uut or broken by the pressure. See figure 

 9 and plate 12. 



' Amer. Jour. Sci.. Mar. 1880. p. 101. 



