ROGERS, GEOLOGY OF THE CORTLANDT SERIES 83 



would the mineral be looked for directly on the contact. It is evident 

 that if the emery is the result of the absorption of the schist, larger masses 

 of the latter might be looked for in the neighborhood, but if the inclusion 

 were small and therefore easily assimilated, they would, of course, not be 

 found. Thus, in some cases we find inclusions of schist near the emery, 

 but never to the writer's knowledge nearer than 200 feet ; and often they 

 are lacking. 



The resemblance of the Salt Hill types of ore to a black quartzose 

 schist has already been remarked upon, and the rough approximation of 

 its strike to that of the schist has also been noticed. In the light of the 

 foregoing facts, it would appear that these occurrences are merely par- 

 tially assimilated inclusions of schist entirely analogous to those so well 

 exposed at Crugers; whereas when the schist is quite absorbed, a much 

 more complex aggregation of minerals results, containing no quartz except 

 in a similar streaky mass at the borders. In the case of the emery pit in 

 the biotite norite area north of Crugers, where the spinel grades into the 

 surrounding rock, this gradation may be thought of as a quick lessening 

 of the effects produced by the absorption of the schist, i. e., the enrich- 

 ment in alumina is naturally merely a local development, although at the 

 same time it can have nothing like a sharp contact. This same statement, 

 of course, applies to similar cases at the other mines. Eeference to 

 Morozewicz's paper, summarized above, will furnish the conditions under 

 which the several minerals must have formed. 



It must not be supposed, however, that anything like a simple direct 

 linear variation exists between the schist and any of the igneous rocks ; a 

 segregational process of some kind must be postulated, for even a richly 

 aluminous schist could not form as a direct hybrid a rock carrying the 59 

 per cent, of A1 2 3 found in the richest emery. Or, since at times the 

 schist retains something of its form and is evidently not entirely absorbed, 

 it may be supposed that the hybrid formed contains the schist constitu- 

 ents in greater quantity than those of the igneous rock. The variation 

 diagram as constructed between mica schist and quartz emery schist and 

 a typical norite shows a distinct approach to linear variation, but if 

 pyroxenite be used instead of norite, the curves are often sharp ; and it is 

 evident that more analyses must be made before the crude process out- 

 lined above can be reduced to an exact determination. 



The final point to be considered — the dynamic action at the mines — is 

 one whose significance is not clear. The fact remains that similar effects 

 are common, though not universal, around the schist inclusions of the 

 district, thus emphasizing a further similarity. It was suggested above 

 by the writer that it might be due to shearing along zones of weakness in 



