574 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. [2j 

 6. Il,LtrSTRATIONS OF EOCK STRUCTURE. 



{a.) Macroscopic. By means of specimens. A series of rocks show- 

 ing all typical forms of structure, as (1) vitreous or glassy j 

 (2) hornlike or flinty; (3)felsitic; (4) granular (clastic); (5) 

 crystalline granular ; (6) aphanitic; (7) porphyritic; (8) mass- 

 ive; (9) stratified; (10) schistose or foliated; (11) fibrous; (12) 

 porous or cavernous ; (13) cellular ; (a) vesicular, (6) pumice- 

 ous; (c) scoriaceous; (14) amygdaloidal; (15) spherulitic; (16) 

 oolitic; (17) pisolitic; (18) concretionary; (19) conglomerated; 

 (20) brecciated. 



(6.) Microscopic. By means of enlarged photographs and draw- 

 ings. A series of colored photomicrographs or hand drawings, 

 showing the ste-ucture of some of the more common rock types 

 as revealed by the microscope. The illustration in all cases to 

 be accompanied by the thin section from which it was pre- 

 pared. 

 Washh^gton, July 21, 1884. 



