PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 435 



Commencing- in the town of Rosendale, there rises up from the valley of 

 the Rondout, and from beneath its bed, a white and rose tinted quartz rock, 

 sometimes very coarse, at others fine grained, and again, in other layers, 

 of a conglomerate character. Locally, it is known as the Esopus millstone 

 grit. It increases in thickness, and gradually ascends, progressing south- 

 wards until, in the town of Rochester, it is from 300 to 500 feet thick, and 

 500 to 600 feet above the level of the valley. It maintains this height, unbro- 

 ken hj a fault or cross valley, to the Delaware water gap, in New Jersey. 

 The anatomy of its laj^ers appears to be these: a, conglomerate, reposing 

 upon the block slate; 6, coarse gray layers, succeeding; c, drab colored 

 layers, often shaly in character; c, white sandstone; d, white pebbles, 

 cemented together; e, white sandstone;/, red colored layers, sometimes 

 shaly, more often sandstone (fossiliferous, rain drops and wave marked). 

 At the base of the mountain are seen the limestone series, which succeed 

 the Shawangunk, sometimes rising into hills, but usually underlaying the 

 valleys of the Rondout and Brasherkill and Neversink rivers. 



Tliis Shawangunk grit is divided up into smaller masses, usually having- 

 well defined angles, by a system of fissures running in lines coincident 

 with the trend of the mountain, and cutting at right angles across it. It 

 is in these fissures that lead, copper and iron pyrites are found. Where 

 the fissure is wide enough to hold an amount of mineral of sufficient econ- 

 omical value to work, there we have a mine, as at Ellenville, Wurtsboro', 

 and the newly discovered vein of the Messrs. Guamaers. This latter is one 

 of these fissures, from two and a half to five feet wide, filled in with claj', 

 rubbish, or broken rock and galena. Its course is up and down the moun- 

 tain, about S. 70° E., and N. 70° W. It is nearly perpendicular, and at 

 this date a shaft has been sunk upon it about thirty feet. Uniformly it 

 bears galena, very compact, of fine grain, and steel gray in color; bi-sulphate 

 of copper, zinc and iron are found with it, but sparingly. Its location is 

 about midway of the mountain, up and down, a few hundred feet from the 

 Erie railroad, above it; and geologically, in the white and gray sandstone 

 layers, immediately below the red layers. 



The regular subject of the evening, " Implements of Modern Warfare," 

 was then taken up. 



Mr. Schoonmaker explained his conceptions of a torpedo to float at any- 

 required depth in the water of a harbor or river: the arrangement of a 

 mirror with a graduated line across it so as to tell by inspection when the 

 vessel of the enemy is exactly over the torpedoes, when they are to be dis- 

 charged by galvanism, with modifications for use and fall of tubes. 



Prof Seely remarked that very quick powder might attain a higher heat 

 during an explosion of a g-un than the 8,400 mentioned by Mr. Wiard, and 

 slow powder less, according to space and previous temperature and con- 

 dition of the material of the gun. 



Mr. Wiard described some recent experiments as to the non-conducting 

 peculiarity of water. He placed a vessel with copper bottom and clay 

 sides on the top of a very hot stove, the vessel filled with lumps of ice and 

 flooded -with cold water. After the vessel had remained there one and a 

 half hours, and after a common tin vessel of cold water had boiled, and 

 was constantly boiling hot, in the same exposure, he found that scarcely any 



