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T 2442 <br /> ca,MMOIAA .With the Lwest.r. <br /> tvh Ln­cong lowerate� rtt <br /> boul.,d t�: �n $ . <br /> ata cad �c imbrian rocl� and fel.si d .a tiffaceou <br /> ; <br /> matrix.teati$. orithe.. ba�s�:uisnt �e� Prcambrfazj racks. <br /> ...... .. .. . . . <br /> tuff.A,must havis..been :S:nte.r�sectad...a.t <br /> ar% unlcnOwr&'ctep-th to the Geyser mine'' works nss because fray- <br /> ments of ouch a tuff are vei~y abundant o.n the mine dip. <br /> This tuff is not exposed at the s.ttrface in the Silver Cliff <br /> ci3.stri ct, ' attd it .is presumably one of .the Lower •beds in the <br /> rhyol,i.ti.c tuff, brecci,a, and conglomerate wni.t„ It ig ' a <br /> pale rod purgle tuff with a prominent autaxiti.c structure <br /> cUused by li.gtlt ,gray, slightly flattened, pumice fra,g„I6nts. <br /> Quartz, bioti,to, and sani.dine crystals; with acwtx dental, pre. <br /> Cambrian• rock fragmentsf are vis3.ble in hand specimelis. <br /> Vitri.c Oards in the matrix can be disti.rgt*i.she by the use <br /> of a hand Ions. Y&croscopi.c ,exa.mi nation shows that the ' <br /> essential, cryatAl,t in order of abundancO are embayed quartz. <br /> a;jd sanjdian+_,• bi.oti.tex zircon and apatite, and .are equal, in <br /> � caequantity, v# the I ii lit -replaced <br /> pumice -11&ag eats. The small a nount of accidental . fragments <br /> i its of Seca nbrian .granite and v crtx.cl.i:ne.- A Uttle <br /> flLvrite,,, rxasqgliably of hydro-thermal, or_3,s in, also occurs. <br /> Glass, shards form the matrix and .are largely i3Ovi.t;ri.fied' to " <br /> 4. . hri,stobaii,.t�, limox�i.tea and al.k&11 feldspar. • The, t4f is <br />