GEOLOGY OF THE NORTH CREEK QUADRANGLE 83 



across, as well as some phlogopite, pyrite, brown hornblende, and a 

 few octahedrons of brown spinel. 



One-half of a mile beyond the northern map limit and near where 

 the road crosses Trout brook there is an old graphite mine which 

 was not visited by the writer. 



Throughout the quadrangle scattering flakes of graphite are 

 rarely absent from the crystalline limestone, and more seldom they 

 are found in other rocks of the sedimentary series. 



MICA 



The only place where mica mining has been attempted is in a 

 large pegmatite dike, which comes against the long gabbro mass 

 on its east side, 2^ miles south-southeast of Chestertown. At the 

 time of the writer's visit (1910) the mine was being worked in a 

 small way by two or three men. While occasionally mica is present 

 in considerable quantity, it seldom occurs in books up to 5 or 6 

 inches across. Muscovite mica is often associated with the peg- 

 matite dikes but thus far no place has been discovered which 

 could really be called a good mining proposition. 



ASBESTOS 



The only attempt to mine asbestos is at the locality three-fourths 

 of a mile southeast of Thurman village. During the summer of 

 1910 large prospect holes had been opened up and mining machinery 

 was being installed, though the writer does not know whether the 

 mine is now in operation. The asbestos is of the serpentine variety, 

 known as chrysotile, and occurs in numerous irregular veins in the 

 greenish gray serpentine marble. Of all the veins noted in the 

 prospect holes, the widest was less than an inch, though wider veins 

 may since have been found. The asbestos is of good quality, but 

 numerous fairly thick veins must be found in order to make a 

 paying proposition of the mine. 



FELDSPAR 



Orthoclase feldspar is of course one of the commonest minerals 

 in the whole region, but only where it occurs in large crystals in 

 the pegmatite dikes is it likely ever to become of commercial im- 

 portance. In all the numerous pegmatite dikes examined, the 

 orthoclase almost invariably occurs in crystals which are too small 

 and too intimately associated with nuich cjuartz and acid plagioclase 

 feldspar to be worth considering as mining propositions. Perhaps 



