BARITE DEPOSITS OF FIVE ISLANDS 787 



also in a fault breccia. The barite is believed to have resulted from a leach- 

 ing and concentration process vrhich took place tnrough the agency of water 

 percolating downward along a zone of faulted and broken rock. The adjoining 

 ledge rocks contain about 0.2 per cent BaO. A comparison with deposits else- 

 where leads to the conclusion that many barite occurrences are the result of a 

 concentrating of the barium content of limestones, sandstones, and quartzites 

 wherever faulting or crushing has made an easy channel for percolating 

 waters. 



FATALITE IN TEE GRANITE OF ROCKPORT, MASSACHUSETTS 

 BY CHARLES PALACHE 



(Abstract) 



A recent discovery of large crystals of fayalite in a granite pegmatite near 

 Rockport furnishes for the first time opportunity for an accurate description 

 of this interesting mineral occurrence, the mineral having been twice before 

 found here, but in neither case studied in place. 



NELSONITE, A NEW ROCK TYPE: ITS OCCURRENCE, ASSOCIATION, AND 



COMPOSITIOm<^ 



BY THOMAS L. WATSON AND STEPHEN TABER 



(Ahstract) 



Nelsonite is the name given to a new rock type occurring in dikelike bodies 

 in the foothills region of the Blue Ridge in Nelson and Amherst counties, Vir- 

 ginia. It forms one of the rock types of a comagmatic area, the rocks of 

 which are characterized chemically by high titanium and phosphorus. Varia- 

 tion in mineral composition gives rise to several different facies of the nel- 

 sonite, the normal one of which is an even granular mixture of essentially 

 ilmenite and apatite, with or without rutile. At several localities ilmenite is 

 replaced by rutile, and the rock is composed chiefly of rutile and apatite with 

 some ilmenite. Green hornblende is occasionally present. The ratio of tita- 

 nium minerals to apatite is variable, ranging from a rock composed largely of 

 the dark minerals with but little apatite to occasionally a rock composed of 

 nearly all apatite. Magnetite replaces the titanium minerals in some of the 

 dikes, accompanied by biotite and apatite. A second pronounced facies of the 

 rock is observed over parts of the area, which shows a predominance of the 

 dark ferromagnesian minerals, more especially hornblende, over the ore min- 

 erals. This variety of the rock is composed chiefly of hornblende, less apatite, 

 and some ilmenite or magnetite. Chemical analyses of the rocks are given 

 and their position in the quantitative system of classification of igneous rocks 

 computed and shown. 



Read by title, In the absence of the authors. 



