ROGERS, GEOLOGY OF THE CORTLANDT SERIES 67 



•count of the water, which fills the pit to a depth of about 30 feet. Just 

 at this level, two adits have been run, at either end of the pit; one of 

 these opens a 30-foot pocket of emery, the other merely runs out on the 

 side of the hill. A derrick was used to raise the ore, which was run down 

 to the road on cars. This was the only place at which an attempt was 

 made to use a steam drill, and it proved a nuisance. The usual method 

 consists of enlarging the cracks in the ore by hand drilling, shaking it up 

 with dynamite and extracting it with pick and bar. 



Williams was the only geologist to discuss the emery in any detail; 

 Dana 52 only briefly mentions it, since in his time it had not been mined 

 except for iron. He notes the thin magnetite beds in diorite on Crugers 

 Point, which Williams has shown to be merely metamorphosed inclusions 

 of schist, 53 and states that the ore is chloritic, whereas Williams 54 has 

 shown in his discussion of the emery that the green mineral is pleonaste. 



The latter, in his first description, states that the veins are segregations 

 in the norite. He describes the ore from a microscopical standpoint, 

 mentioning the various minerals which the present writer describes below ; 

 and gives seven analyses of the emery, partly chemical and partly physical, 

 but makes no mention of the localities from which the specimens were 

 taken, or what varieties they were, etc. In his paper on contact meta- 

 morphism, however, he abandons his former view. To quote : 55 "The 

 isolated inclusions (i. e., the metamorphosed schist inclusions at Crugers) 

 of spinel and corundum are almost identical with the more extensive de- 

 posits of the same character occurring near the southern border of the 

 norite region farther to the east and described at length in a former 

 paper. Their origin in both cases is without doubt essentially the same." 



It is somewhat unfortunate that his previous view, based on fewer 

 observations, should have found its way into the literature. 



J. H. Pratt 56 gives a condensed account of Dana's work and of Wil- 

 liams's work on the norites and evidently relies largely on the latter for 

 his statement that the emery is probably due to segregation in the norite 

 along the borders of the magma, in a fashion analogous to that of pyrrho- 

 tite, etc. The fact which sustains this view is given as the "gradual 

 transition of the spinel, iron ore and emery into the normal norite" — a 

 fact observed by Williams. He does not appear to have consulted Wil- 

 liams's other papers; but from the description of the series given above, 



52 Amer. Jour. Sci., (3), XX, 199-200. 1880. 

 "Amer. Jour. Sci., (3), XXXVI, 261 et seq. 1888. 

 "Atner. Jour. Sci., (3), XXXIII, 194-199. 1887. 

 55 Loc. cit. 



59 Corundum and its Occurrence and Distribution in the United States, Bull. 269, U. S. 

 G. S., pp. 41, 93 and 137. 1906. 



