338 J. S. Diller — Origin of Paleotrochis. 



of Paleotrochis. The specimens he examined were those 

 obtained by Prof. Emmons, as well as a number collected by 

 Prof. J. A. Holmes, the present State Geologist of North Caro- 

 lina. Mr. White describes in detail not only the peculiarities 

 of the weathered surface of the rock but also the features 

 exhibited upon a fresh fracture, and called attention for the 

 first time to the radial fibrous mineral which he regarded as 

 impure chalcedony. According to Mr. White, the fossil forms 

 are enveloped in chalcedony and the small concretions are made 

 of the same material. 



In 1887, Prof. J. A. Holmes* visited the Sam Christian 

 Gold Mine of Montgomery County, N. C, and studied the 

 Paleotrochis-bearing rock in the field. Although he had not 

 then seen any of the acid volcanic rocks from JNew England, 

 described by Dr. M. E. Wadsworth, or from the South 

 Mountain region of Maryland and Pennsylvania, subsequently 

 described by Dr. G. H. Williams and Miss Florence Bascom, 

 he was of the opinion that the rocks in the neighborhood of 

 the Sam Christian Gold Mine were of eruptive origin. Later 

 observations have convinced him of the correctness of this 

 view. The same opinion is entertained by Messrs. H. B. C. 

 Nitze and George B. Hanna,f who consider the Paleotrochis- 

 bearing rocks at the Sam Christian and Moratock Mines as 

 ancient acid volcanics } and state that " it appears highly prob- 

 able that at least some of these siliceous pebbly concretions are 

 spherulites." Unfortunately in the preparation of their report 

 time did not permit the authors to study thin sections. 



The specimens which, at the request of Mr. C. D. Walcott, 

 the Director of the U. S. Geological Survey, the present 

 writer has had an opportunity to study, consist of a small col- 

 lection^: from Mexico sent by Prof. H. S. Williams, besides 

 three fragments about nine inches in diameter sent by Prof. J. 

 A. Holmes, who collected them in 1887 at the Sam Christian 

 Gold Mine, North Carolina, and from the same place several 

 dozen of the original specimens of Paleotrochis major and 

 minor collected by Prof. Emmons. Specimens of the rock 

 and isolated fossils, excepting those from Mexico, have been 

 cut and polished and thin sections prepared for microscopical 

 study. 



The rock from North Carolina which contains Paleotrochis 

 is full of nodules of various shapes and sizes, ranging from 

 that of a pin's head to nearly two inches in diameter. These 

 are the supposed concretions and fossils. Upon a fresh fracture 

 the rock appears to be composed chiefly of quartz, but when 



* Letter to the author Feb. 6, 1899. 



+ North Carolina Geological Survey, Bui. No. 3, pages 37 and 39. 



% See Prof. William's article, this volume, page 335. 



