HISTORY OF GEOLOGICAL SURVEY. 39 



correspond with that in Franconia about the Lafayette range, our former 

 ideas must be modified. We should have, therefore, an underlying gran- 

 ite, as seen in Mad river two miles below Greely's hotel ; then the trachytic 

 granite of Osceola, extending to the cascades and including the "nodular 

 gneiss" on Norway brook, dipping gently westerly; and finally above 

 both, the ossipyte schists, with a small inclination. 



Mr. E. S. Dana has carefully analyzed specimens of the Waterville 

 rocks, and described the assemblage as a new rock, with the name of 

 Ossipyte, after one of the aboriginal tribes of Indians formerly dwelling 

 in the neighborhood. 



The following are his results with the ossipyte, it being composed of 

 the two minerals, labradorite and chrysolite : 



100.37 



The large percentage of iron (determined volumetrically) had not been expected, 

 as the eye had failed to detect any impurities in the fragments selected for analysis. 

 Some very thin pieces were afterwards examined under the microscope ; and by this 

 means it was found that even the clearest pieces contained very minute grains of an 

 iron ore, from -g^th to -^oth of an inch in diameter, which were strongly attractable by 

 the magnet. Microscopic dark specks less than T o-oTo^ 1 of an inch in size were also 

 observed, and at first referred to the same cause ; but, on magnifying them 800 diame- 

 ters, it was concluded that they were air-cavities in the structure of the feldspar, and 

 not any foreign matter. The peculiar dark smoky color of the rock is doubtless to be 

 explained by the presence of these particles of iron ore. 



This magnetic iron ore, a sufficient amount for the test having been picked out 

 by the magnet, gave a decided reaction for titanic acid. 



2. Chrysolite. 



100.08 100.35 100.21 



