ROGERS, GEOLOGY OF THE CORTLANDT SERIES 81 



important variety, unless indeed Sewage after the separation of the emery 

 is postulated. Finally, the abundant garnets found at the Chase mine 

 are not explained, nor the biotite at the McCoy and Chase mines ; nor is 

 the association of the emery with quartz accounted for. It would be diffi- 

 cult to explain how corundum could separate in the presence of quartz, 

 since according to Morozewicz the two would combine to form sillimanite. 



Theory of the Absorption of Sedimentary Material 



The possibility of the effectiveness of the absorption of sedimentary 

 material is evidenced by the fact cited above from Morozewicz, viz., clay 

 crucibles are attacked at a high temperature by melts rich in MgO and 

 poor in A1 2 3 and alkalis, such as pyroxenite. If this could take place at 

 2100° C. with a low pressure, it appears certain that a molten magma of 

 such composition could readily attack a more or less attenuated inclusion 

 of mica schist; and the abundance of these inclusions in the district has 

 already been shown. 79 Lacroix, 80 moreover, states the following general 

 rule : "Si l'enclave differe beaucoup de la roche eruptive par sa teneur en 

 silice, elle est facilement detruite et l'on n'en trouve plus, en general, que 

 des traces/' This principle had been applied by him in Haute Loire and 

 by Pirsson at Yogo, Montana. 



In such a case, the process would involve the separation of a small mass 

 of aluminous sediment and its more or less complete absorption by the 

 subterranean magma. This would give rise to a local enrichment in 

 alumina, which would then be deposited according to the laws enunciated 

 by Morozewicz. The theory thus involves certain features of both mag- 

 matic segregation and contact action, but it is essentially neither; nor 

 does it involve the old view which Morozewicz and Lagorio have shown to 

 be false, that corundum is infusible in a magma and that it merely repre- 

 sents the unattacked portions of the xenolith. The occurrence is taken by 

 the writer to be a strong confirmation of the laboratory experiments of 

 these geologists, rather than to oppose them. 



The accompanying analysis of mica schist was made with a view to de- 

 termining the extent to which this rock could have contributed alumina. 

 The percentage found (21.70) is only slightly above that in the norites; 

 pure norite (which is chiefly feldspar) reaches 20.72 per cent., being the 

 highest. The pyroxenites in which the ore is generally found run about 



79 In this connection, also, the limestone inclusions of the district, altered to lime 

 pyroxenite in one case, wernerite schist in another and a garnet-tremolite rock in a third, 

 may be recalled as indicating the capability of the igneous rock to absorb and work over 

 an included mass. The fact that most of the inclusions of schist practically lack mica, 

 which must have been absorbed by the magma, may also be recalled. 



80 Op. cit., p. 101. 



