514 



REPORT OF NATIONAL MUSEUM, 1890. 



3. Types of colloidal rock : 



(I) Siliceous sinter, (Pealite),. Yellowstone National Park. 28964 



(II) Opal, Rapides Parish, Louisiana. 38612 



(III) Flint, England. 36012 



(IV) Serpentine, Montville, New Jersey. 39038 



(1) Tufaceous structure : 



Calc tufa, Yellowstone National Park. 72861 



(2) Botryoidal structure : 



Chalcedony after coral, Florida. 39051 



(3) Concretionary structure : 



(a) Oolitic limestone. Cache Valley, Utah, 35305 



(&) Pisolitic limestone, Pyramid Lake, Nevada. 35306 



(c) Siliceous concretions, Yellowstone National Park. 12888 



(4) Cellular structure : 



Buhr stone, Sevastopol, Georgia. 36051 



4. Types of fragmental rock : 



I. Coarse sandstone, Deerfield, Massachusetts. 26144 



(1) Granular structure : 



Sandstone, Berkshire, Massachusetts. 72798 



(2) Compact structure : 



Sandstone, Hingham, Massachusetts. 35939 



(3) Laminated structure : 



(a) Slate, Poultney, Vermont. 27183 



(&) Sandstone, Fort Collins, Colorado. 35998 



(4) Banded structure : 



Shale baked by trap dike, Deckertown, New Jersey. 36767 



(5) Concretionary structure : 



Coquina, St. Augustine, Florida. 28662 



(7) Conglomerated structure : 



Conglomerate, Beltsville, Maryland. 25647 



(9) Brecciated structure : 



(a) Calcareous Breccia, Vitulaud, Italy. 36109 



(5) Siliceous Breccia, Yellowstone National Park. 37924 



The following show the types of labels used in these series : 

 Vitreous Bocks. 



VESICULAR STRUCTURE. 



Obsidian Pumice. 



Mono Lake, California. 29,630. 



Collected by G. K. Gilbert, 1883. 



B. Microscopic structure. — Shown by twelve transparencies in the 

 windows. 



The circular transparencies in the windows are designed to show the 

 microscopic structure and mineral composition of the nior-e common 

 types of rocks. In preparing the transparencies a small chip from 

 each rock was ground so thin as to be transparent (from -gfo to ^q of 

 an inch), and then after being mounted between thin slips of glass was 

 photographed through a microscope and between crossed nicol prisms. 

 From the negatives thus prepared further enlargements were made by 



