484 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. 37. 



EXPLANATION OF PLATE 37. 



Upper Figure. Olivine-diabase from Davidson County, North Carolina. A photo- 

 micrograph in ordinary light, magnified about 20 diameters. 

 Section shows plagioclase laths, augite, and olivine; the last 

 altering to talc. The ophitic texture is well illustrated. 



Lower Figure. Olivine-diabase from Davidson County, North Carolina. A photo- 

 micrograph in polarized light, with crossed nicols, magnified 

 about 20 diameters. Shows twinned plagioclase, augite, and 

 grains of olivine. 



