392.] Mineralogy and !'■ 



apposed to have originated by the gradual deo 

 nclosed in the ash. Hatchings' records the ex 



nd garnet in the flags at Shap, England, where th 

 iv the intrusion of granite through them. The ti 

 n the contact zone within the zone of Bpotted data 



it is probably andalusite. The clay slate needles that arc present m 

 large quantity in the unaltered flags continue to exist even in those 

 mcks in which brown mica lias hegun to form. In the phases in winch 

 brown mica is abundant and newly-formed quart/, is present the 

 needles have disappeared, and in their place arc found crystals and 

 grains of rutile and sphene. In another stage of the contact action 

 groups of large rutile crystals are observed, and in the neighborhood 



of spots are clusters of anatase crystals. In central Liberia are 



mighty dykes and flows of basic rocks, among which Chrustschoff 1 

 recognizes ten types of augite — plagioclaae — olivine rocks, containing 

 more or less orthorhombic pyroxene and orthoclase. Their structure 

 varies from the gabbroitic to the basaltic. Each type i, described in 

 detail and a photograph of it appears with the description. ^ Even in 

 the most glassy varieties well developed orthoclase exists. The prin- 

 cipal structures noted are the gabbroitic, ophitic, with and without 

 glassy base, anamesitic and aphanitie. with small crystals of feldspar. 



Mr. Rutley" describes verv briefly a few sections of basalt or ande- 



sitic glass from CaradocHilL in Shropshire, Eng. At present the rock 

 contains no olivine, but certain peculiar arrangements of magnetite 

 grains indicate its former existence in them. With the glass are a 

 basalt tufa and perlitic tebitic rhyolites with obscure flowage struc- 

 ture, and some with spherulites. An interesting sphen.Iit.c and per- 

 litic obsidian is also described by the same i 



> Pi,,-. \h 



■ 



In this the perlitic cracks were certainly tornu 

 spherulites, and were afterwards filled with secondary silica and per- 

 haps other substances. Much of the so-called anthophylhte and 



the rock s associated with the iron ores of the Lake .super- 

 ior region is a monocliuic magnesian amphibole, corresponding togru- 



