BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



VOL. 16, PP. 131-136, PLS. 33-34 MARCH 10, 1905 



ON THE ORIGIN OF VEINS IN ASBESTIFORM SERPENTINE 



BY GEORGE P. MERRILL 



(Read before the Society December SO, 190 Jf) 



CONTENTS 



Page 



Introduction 131 



Description of the specimen 131 



Origin of the vein cavities 133 



Filling of the vein cavities 136 



Introduction 



As a result of a recent trip to Thetford mines, in Canada, the writer 

 was able to secure for the National Museum, and through the courtesy of 

 Mr B. J. Bennett, manager of the King Brothers mines, an unusually 

 fine block of serpentine, with veins of the fibrous form, chrysotile (the 

 so-called asbestos), which seems worthy of a special description, even 

 though little, if anything, new is deduced relative to the origin of the 

 material. 



Description of the Specimen 



The block, as now on exhibition in the Museum (plate 33), is some 

 30 by 30 by 27 inches (76.2 by 76.2 by 68.6 centimeters) in dimensions. 

 As seen in the plate, it is traversed from left to right by one large vein of 

 the asbestos (chrysotile), with others not quite so wide, in an approxi- 

 mately vertical direction. 



Confining our attention first to the horizontal vein (some 40 millime- 

 ters in maximum width), it will be noted that the fibers are not in all 

 cases continuous from wall to wall, but that they are intercepted about 

 midway by a narrow band of massive material, which shows only as a 

 dark wavy line in the illustration. This is a very common occurrence. 



Though the vein is separated sharply from the massive material, there 

 are numerous short, narrow veinlets, some almost microscopic, extending 

 into it from either side, above and below. These are not over 20 to 40 

 millimeters in length and 1 to 5 millimeters in width. Referring to the 



XVIII— Boll. Geol. Soc. Am., Vol. 16, 1904 (131) 



