PRELIMINARY HANDBOOK OF THE DEPARTMENT OF GEOLOGY. 13 

 II. — DYNAMICAL AND PHYSIOGRAPHICAL GEOLOGY. 



Under this section are discussed tbe agencies and methods of geo- 

 logical change. It is of course impossible to represent these agencies 

 in actual operation, and we must confine ourselves to a display of 

 results which the labels explain. In this section are placed those 

 objects illustrative of (1) Plutonic or hypogene action, under which are 

 included (a) volcanoes and volcanic action, (b) earthquakes, (c) secular 

 upheaval aud subsidence, and (d) hypogene causes of chauges in the 

 texture, structure, and composition of rocks; and (2) epi gene or surface 

 action as illustrated by the destructive and constructive or reproduc- 

 tive action of the atmosphere, water, and life iu its various forms. 



(1) Plutonic or hypogene action (Geikie, pp. 178-294). — Volcanoes and 

 volcanic action are illustrated by a small (2 feet 4£ inches square) model 

 of Vesuvius and Monte Somma, Italy, and which is accompanied by a 

 collection illustrating the character of the ejectamenta. This includes 

 the lavas of 1631, 1760, 1855, and 1872; ejected and altered blocks of 

 limestone (73965, 72966, 72968, and 72969); ashes, sand, and dust, in- 

 cluding the pumiceous materials such as overwhelmed Pompeii (73149); 

 decomposed ash from the crater of 1872 (72988) ; lapilli from the cone 

 of 1880 ; hematite with chlorides of iron, copper, potash soda, magnesia 

 (72993) ; cupriferous sylvite (73032) ; sulphur and other sublimation or 

 solution products. Under this head is also exhibited a fine example of 

 the siliceous cones built up by the geysers of the Yellowstone National 

 Park (35590) ; the calcareous cones sometimes formed by hot springs 

 (10809), and a diminutive cone of a mud volcano from the same region 

 (12879). The varying character of volcanic ejectamenta is shown by a 

 remarkably fine series of basaltic lavas iu large specimens from the 

 now extinct volcanoes of Ice Spring Buttes, Utah (35371-35371), aud 

 the Hawaian Islands (35849-35851), including a cake of lava dipped by 

 Dr. Judd from the crater of Lua Pele (12823) ; and by acid compact and 

 pumiceous glassy lavas (obsidians) from Mexico (35780) and the Mono 

 craters, California (29630 to 29631). 



There are also numerous smaller specimens from Vesuvius and other 

 active volcanoes. The fragmental material ejected (Geikie, p. 186) is 

 illustrated by ashes and sand ejected in 1883 from the volcano on Bo- 

 gosloff Island (37034); by pumice dusts which, when blown from the 

 vent, are often drifted long distances by the winds (37207) ; lapilli, such 

 as frequently make up the volcanic cones (35538), and quite a series 

 of bombs, including specimens from the Auvergne (39130); the Eifel 

 (38755); Brazil (69988); the Hawaian Islands (7056S); a pumiceous 

 bomb from Vulcauo on the island of Lipari exhibiting the so-called 

 bread-crust structure (73163); a large flattened bomb picked up one- 

 half mile from the crater at Ice Spring Butte (35373); a typically elon- 

 gate globular-shaped bomb from Mount Trumbull in Arizona (70586), 

 and two peculiar basaltic bombs with large angular inclosures of grau- 

 ular olivine (70585) from the same region. The exhibit is supple- 

 H. Mis. 224, pt. 2 57 



