PETROGRAPHY 



335 



in many cases that the serpentine is secondary after pyroxene, but 

 some forms of serpentine seemed to him not to be referable to this 

 original. In my slides, the core of pyroxene is usually present and 

 the process of alteration is graphically shown. The total effect 

 resembles an altered olivine crystal most closely. In one instance 

 the core proved isotropic and showed no trace of an optic axis. It 

 would appear to be an isometric mineral of quite high index. 



The limestone series is accompanied by masses of silicates of all 

 sizes from small bunches up to large lenses. There are also beds of 

 dark schistose rocks that are an inseparable associate, and no 

 extended section was met devoid of them. The small bunches are 

 especially numerous near the contacts with gabbros, and in the 

 Delaware and Hudson railway cuts, two miles and less above Port 

 Henry, along the lake they are very numerous. They assume very 

 fantastic shapes, from the small foldings and stretching of the lime- 

 stone, and specially resemble snakes. These are here regarded as 

 due in part to the metamorphism of siliceous portions of the original 

 limestone, but still more often to bunches of minerals formed by 

 contact action along the intruded gabbro. They have been after- 

 wards stretched in the general dynamic disturbances which have 

 given rise to such extended foliation. The limestone everywhere 

 gives evidence of being very plastic under these conditions and has 

 wound itself around the inclusions and followed them in many 

 intricate curves. 



The inclusions exhibit in thin section, plagioclase and hornblende 

 in greatest amount, and with these phlogopite, scapolite, pyroxene, 

 quartz and probably orthoclase. In larger ones fine crystals of 

 brown tourmaline and light brown hornblende, titanite and rather 

 rudely bounded pyrrhotite appear. All these show characteristic 

 forms. Yery similar mixtures are met at Yan Artsdalen's quarry 

 near Philadelphia, Penn. as has been cited by the writer (Trans. N. 

 Y. Acad. Sci. Yol. XII. p. 74, Jan. 23, 1893) where they are referred 

 to the contact action of gabbro. They are practically duplicated in 

 the bunches of silicates contained in the marbles on the contact with 

 the hornblende granite of Mount Adam and Eve, Orange co. X. Y. 

 A very complicated and interesting mass of silicates occurs in the 

 cut on the railway from Port Henry to Mineville, just at the grade 

 crossing of the northeastern highway in 08, of the map. Garnet, 



