/ 



) 



364 On the Houghite of Prof, ^hepard. 



These accordant results indicate the existence of definite rela- 

 tions between these two ingredients. Divison'by the equivalents^ 

 gires the ratio of 4 of alumina to 19 magnesia, corresponding to 

 alumina 35- 15, magnesia 64-85. The ratio of 1 : 5 would require 

 alumina 33'53j magnesia 66'47. 



It seems useless to speculate on the constitution of Houghite 

 without new analyses. 



Q.uite recently, I have visited the locality in company with Dr. 

 Hough. It is in the town of Rossie, and near the village of | 



Somerville, in St. Lawrence county, N. Y. The mineral occurs 

 disseminated through white crystalline limestone, at the summit i 



of a slight elevation, near which occurs beds of the Potsdam 

 sandstone. Associated with Houghite are dolomite of variable 

 composition, scapolite of brown and green color, phlogopite, 

 graphite, spinel, and a crystallized pseudomorphous(?) yellow 

 serpentine, in which I have obtained the water and silica per- 

 centages of that mineral. 



Much of the rock exhibits evidences of atmospheric action- 

 The serpentine in the altered parts has become discolored and so 

 friable as to yield to the pressure of the fingers. The nodules of 

 Houghite are half exposed, easily detached from the rock, and 

 often opake and milk-white throughout. 



This altered or bleached appearance in the rock does not occur 

 upon the uppermost surface, as far as I have observed, but along 

 its sides and under portions pendant over a cavity. But not a 

 nodule of Houghite has been found even in the least ahered 

 rock that has not presented superficially in some parts a milk- 

 white color. 



Among the masses which furnished material for analyses, I 

 found several specimens that exhibited unequivocal evidences of 

 octahedral crystallization, one of which is 

 here represented. Some of them are fths 

 of an inch in diameter; they are superfi- 

 cially grooved and contorted, their edges 

 are rounded, and protrude beyond the 

 planes of the faces. In some an appear- 

 ance occurs, which seems as if it had been 

 produced by a protrusion, near the edge of 

 each plane, leaving a line of depression 

 with reentering surfaces, corresponding to 

 the lateral edges of a perfect octahedron, 



while on the faces, a triangular depression occurs, bounded by the 

 protruded edges of each plane of the crystal. In one nodule 

 there is a gradual transition from the soft and amorphous Hough- 

 ite, to the hard and regularly terminated spinel The crystals are 

 occasionally compound. 



