HANDBOOK FOR THE DEPARTMENT OF GEOLOGY. 539 



nuted materials ejected from volcanoes as ashes, dust, and sand. Some 

 of them, like the puinice dust from near Orleans, Nebraska (specimen 

 No. 37023), are made up of minute shreds of puiniceous glass. These 

 are the dust-like materials which, when blown from volcanic vents, are 

 carried by atmospheric currents many miles and deposited so far from 

 their original source that their true nature was never recognized until 

 they came to be examined microscopically. (See under iEoliau rocks.) 

 Others, like the lapilli from the now extinct craters at Ice Spring 

 Butte (specimen 35538), are irregular fragments of basaltic lava which 

 when thrown into the air fell again into the immediate vicinity, forming- 

 beds of loose gravel and the cone of the crater itself. The character of 

 the materials, therefore, varies almost indefinitely, and only very gen- 

 eral names are given them in the majority of cases. The name tuff or 

 tuffa is given to the entire group of volcanic materials formed in this 

 way, and also by some authorities to frag mental rocks resulting from 

 the breaking down and reconsolidatiou of older volcanic lavas. It 

 would seem advisable to designate these last, as has F. Lowiuson-Les- 

 sing,* as pseudotuffs or tuffoids. Characteristic forms of the tuffs are 

 shown in the collections, and need not be especially enumerated here. 

 The names volcanic ashes, saud, and dust are applied to the finer mate- 

 rials ejected and lapilli or rapilli to the coarser fragments like those 

 from the extinct volcanoes of Ice Springs Butte, Utah (35538); Mono 

 craters, California (29633) ; Pompeii and Monte Vultura, Italy (36603, 

 38794, and 38797). The finer dusts and saud, such as shown from Ne- 

 braska (37023 and 37024), Utah (37261), Montana (38584 and 38585), are 

 of interest as being composed of minute shreds of volcanic glass which 

 were blown from the volcanic vents and carried unknown distances to 

 be ultimately deposited as stratified beds in comparatively shallow 

 water. (See collections illustrating the transporting power of atmos- 

 pheric currents.) The term trass is used to designate a compact or 

 earthy fragmental rock composed of pumice dust, in which are imbedded 

 fragments of trachytic and basaltic rock, carbonized wood, etc., and 

 which occupies some of the valleys of the Eifel (specimen 36355 from 

 Brohlthal, Prussia). Peperino is a tufaceous rock composed of fragments 

 oi basalt, leucite lava, and limestone, with abundant crystals of augite? 

 mica, leucite, and magnetite. It occurs among the Alban Hills, near 

 Rome, Italy. Palagonite tuff is composed of dust and fragments of 

 basaltic lava with pieces of a pale yellow, green, reddish, or brownish 

 glass called palagonite, as shown in specimens 36501 and 34739 from 

 Nassau, Germany, or 36507 from Sicily. The general name of volcanic 

 mud is given to such materials as that from Paterno, Sicily (73024). 



The tuffs are as a rule more or less distinctly stratified, of very un- 

 even texture, and with rarely a pisolitic structure as shown in the 

 specimen from Nevada (35406) and Pompeii (73025). They are found 

 associated with volcauic rocks of all ages and at times so highly nieta- 



*Min. u. Pet. Mittheilungen, vol. 9, 1889, p. 530. 



