I Id .1. S. DILLER — SANDSTONE DIKES 



.1. I). Whitney, in bis Geology of California, vol. I, p. 40, saya that at 



L Tree cafion, about Beven miles southeast of Corral Hollow, California, 



■■ ma — of sandstone were found in the shales in tin- same position with 

 reference to the Biirrounding rocks a- would be occupied hy dykes. Th< 

 dyke-like ma- - - m to have originated in the filling of figures by Band 

 which has since become indurated." Professor W. II. Brewer, who appears 

 t<> have made the observations upon which Professor Whitney's Btatement is 

 based, discovered these dikes in middle California nearly thirty years ago; 

 and it is probable that others will he found in that country of earthquak 



Several years ago .Mr. C. D. Walcott collected, near Lake Champlain, a 

 Bpecimen from what he at the time regarded as a dike cutting limestone. 

 We were much surprised at the time upon examining a thin section of the 



rock to find it sandsl s. In general it resembles the sand-tone dike rock 



of California, hut none of the few scales of mica in the section were found 

 to lie crushed. 



Several weeks ago Mr. \V J McGee discovered a number of Bmall saml- 

 Btone dikes intersecting the Eocene Buhrstone at Corinne, in eastern-central 

 Mississippi. Mr. McGee kindly permits me to announce this interesting 

 find, and has furnished material for examination not only from the dikes 

 hut also from their country rock. < >ne dike is s to 1 L' inch.- in thickm 38, 

 and another i> 1 inches. Specimens were collected from both dikes. They 

 an- distinct sandstones to the naked eye, light-colored, almost white, except- 

 ing where stained yellow by oxide of iron. In the thicker dike the sand 

 i- firmly lithified, while in the thinner it is rather friable. Both Bides of the 

 thicker dike are ■' distinctly slickensided vertically," though there is no per 

 ceptible displacement of the Btrata in the country rock. 



The most conspicuous mineral in' the hand specimens of these dike-, as in 

 those of < lalifornia, is mica. In ( lalifornia it is biotite, hut in Mississippi it 

 i- muscovite. Another feature which may he Been in the hand specimens i- 

 that the scales of mica are all approximately parallel, not only among them- 

 selves, hut also with the side of the hand specimen which Mr. McGee informs 

 me was the aide of the dike. 



Thin sections were prepared of the dike rock in two directions perpen- 

 dicular to each other and both at right angles to the sides of the dike. The 

 rock, is composed chiefly of grains of quartz sand, which in many cases ha 

 been partially rounded. It is of the kind of quartz that is common in granitic 

 rock- and occasionally contains minute scales of biotite and -mall dark 

 needles which are well known in granitic quartz. One -rain was observed 

 apparently with several glass inclusions, such a- are known in the quartz 

 of eruptive rocks only. ' Occasionally grains of tourmaline are found inter- 

 mingled with the quartz 



Muscovite, although rather plentifully present, is far less abundant than 



