MODE OF OCCURRENCE 465 



completed; but important results that are definite have followed from 

 the investigation^ which are set forth in this paper and will doubtless 

 form the basis of future study. 



During the progress of the laboratory investigation on this problem 

 Mr. George L. English, of Eochester, 'New York, and Dr. D. F. lN"ewlaiid, 

 Assistant State Geologist of Few York, very kindly placed at the writer's 

 disposal specimens of allanite from Pennsylvania and ISTew York. Among 

 the specimens donated by Mr. English were additional ones from localities 

 in western North Carolina and from the new locality in Anderson County, 

 South Carolina. The allanite from Chester County, Pennsylvania, and 

 that from Ellenville, New York, exhibited the usual form of weathering. 

 Analyses of the weathered product of the allanite from these localities 

 could not be completed for this paper, but the results of the microscopic 

 study are included. In each case the microscope showed similarity in the 

 heterogeneous character of the weathered product. 



While the results of microscopic study of the decomposed product of 

 allanite are based on material from many widely separated localities in 

 the eastern United States, chemical analyses are necessarily more re- 

 stricted and are limited in this paper to unusually good material from 

 several Virginia localities. After examination of similar material from 

 other localities in the eastern United States and abroad, the Virginia 

 material is considered to be representative for. allanite Aveathering in 

 general. 



For the purposes of this paper and for future studies of allanite a care- 

 ful search has been made of the literature relating to the occurrence and 

 distribution of the mineral in the eastern United States and the results 

 are briefly summarized herein. 



Mode of Occurren'ce of Atj.anite 



Our present knowledge of allanite indicates the principal conditions 

 under which it is formed to be a constituent of (1) igneous rocks, (2) 

 pegmatites, (3) contact metamorphism, and (4) dynamo-regional meta- 

 morphism.2 Of these, the occurrence of allanite in pegmatites is the 

 most important, since the mineral is usually developed in largest masses 

 and in greatest quantity. 



For many years allanite was regarded as a rare rock-forming mineral, 

 but the investigations of Iddings and Cross^ in 1885 demonstrated its 

 wide distribution as a primary accessory constituent of many igneous 



2 W. H. Emmons : Economic Geology, vol. iii. 1908, pp. 611-627. 



3 J. P. Iddings and W. Cross : Am, Jour. Scl.. 3d ser., vol. xxx, 1885, pp. 108-111. 



