280 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1921. 



and 8,500 feet above sea level. (See pi. 14.) In addition to the 

 wonderful scenic effect consequent to these altitudes, the park owes 

 much of its interest to the evidence of recent and dying volcanism, as 

 displayed in its hot springs and geysers, lava flows, fossil forests, and 

 associated phenomena. The collection shows by means of the relief 

 map, specimens, and photographs, including transparencies in the 

 windows, such examples of the park phenomena as lend themselves to 

 display. The material has been acquired through many sources. 

 The U. S. Geological Surveys, Supt. P.-W. Norris, in 1881, and Sec- 

 retary and Mrs. Walcott in 1915, collected a considerable part of the 

 quartz groups and sinters. Of particular interest are the siliceous 

 geyser cone and the large fungoid-shaped siliceous sinters, the basaltic 

 column, silicified woods, and masses of quartz (sometimes amethys- 

 tine) and chalcedony. 



CONCRETIONS AND SEGREGATIONS. 



The exhibit includes a series of more or less spherical bodies which 

 owe their forms in part to physical and in part to chemical agencies. 

 These are commonly known as concretions, though in many instances 

 the word segregation is more nearly applicable. Indeed, in some in- 

 stances neither term is strictly correct, since the concretionary struc- 

 ture is wholly simulated. 



In the arrangement of the collection the following scheme of clas- 

 sification has been adopted : 



I. Concretionary form due to crystallization from a mol- 

 ten magma. Examples, the concretionary or spherulitic 

 granites from Finland and Sweden (pi. 15, fig. 2). 



II. Concretionary form due to precipitation from solu- 

 tion, with or without crystallization. Examples, large sep- 

 tarian nodules and chert-concretions in limestone. 



III. Concretionary form due to segregation of solid parti- 

 cles, with or without a cement or binding constituent. Ex- 

 amples, the clay concretions from the Connecticut River. 



IV. Concretionary form due to weathering and cemen- 

 tation; secondary. Example, the concretions of ferrugin- 

 ous sand from Maryland. 



V. Concretionary form due to local cementation of beds 

 and subsequent weathering away of uncemented portions; 

 pseudo-concretions. Examples, the large spherical sand- 

 stone forms from the Cannon Ball River. 



VEINS AND DIKES. 



The term vein is commonly applied to fractures in rock masses 

 which have become filled with secondary minerals deposited from 



