ON OLIVINE-DIABASE FROM DAVIDSON COUNTY, NORTH 



CAROLINA.^ 



By Joseph E. Pogue, 



Assistant Curator, Division of Mineralogij, U. S. National Museum. 



Introduction. — The terms ''basalt" and " diabase " have been em- 

 ployed with varying significance in this country and abroad. By 

 diabase, as used herein, is meant a basic igneous rock, composed 

 predominantly of plagioclase and augite, having ophitic texture, and 

 occurring in dikes or intrusive sheets. Where olivine is present as 

 an essential constituent the rock is termed an olivine-diabase. 



Olivine-diabase, though by no means a rare rock, has not the 

 wide distribution of the olivine-free members of the diabase family. 

 In the United States it has been described, in more or less detail, as 

 occurring at St. George (5),'' Kennebunkport (12), Addison Point 

 and Vinalhaven (18), Maine; in the Lake Champlain region (13); 

 at Deerfield (7) and Cape Ann (22), Massachusetts; among the 

 Thousand Islands, in the St. Lawrence River (24) ; in the Palisades of 

 the Hudson, in New Jersey (16, 17); in Culpeper (1), Floyd (27), 

 and Pittsylvania (28) counties, and near Harrisonburg (4), Virginia; 

 in Rowan (14) and Davidson (21) counties. North Carolina; in Lee 

 County, near Gold Hill, Alabama (2) ; in the Diablo and Van 

 Horn mountains of Texas (19); near Pilot Knob and Iron Mountain, 

 Missouri (10); in Minnehaha County, vSoutli Dakota (3); at Pigeon 

 Point, Cook County, Minnesota (6), and a number of localities near 

 Brule River and Duhith (26) ; in the Marquette iron-bearing district 

 of Michigan (25) and the Penokee series of Michigan and Wisconsin 

 (11) ; in California, near San Luis (8) and in the San Francisco penin- 

 sula (15); in Kittitas County, Washington (23); and in Alaska near 



"The data for the present paper are taken largely from a report, by the writer, 

 on the Cid mining district of Davidson County, North Carolina, which is now in press 

 and will appear as Bulletin No. 21 of the North Carolina Geological Survey. For 

 this privilege the author is indebted to the courtesy of Dr. Joseph Hyde Pratt, the 

 state geologist. 



& The numbers in parentheses refer to the bibliography at the end of the article. 



Proceedings U. S. National Museum, Vol. 37— No. 1715. 



475 



