BY W. X. BENSON. 373 



cracks. Analogous specimens occur elsewhere, generally not so 

 oxidised. 



The complex of magnet it e-keratopliyres at tiie liead ol Bog Hole 

 Gully, contains the same \ ariety of rocks as does that near Hyde's 

 Creek, previously described (5, pp. 150-151). 2\odular kerato- 

 pliyres occur (No. 1410), in which the rock is made up oi' frag- 

 ments oi' trachytic keralophyrc, \ery euriched in magnetite in the 

 centre oi' each iragment, but Tree Irom it at the margin. Between 

 the fragments are strings of more coarsely crystalline keratophyrc 

 and calcite, apparently introduced at tiie same time as the second- 

 ary magnetite, i.e., during or inmiediately after the brecciation. 

 Theealeite is thus to be considered as derived from the magmatie 

 solutions. In another example (No. 1120), the magnetite-kerato- 

 phyi'e is amygdaloidal, the vesicles containing calcite or quartz, and 

 deep green epidote, and occasionally large grains of magnetite. 

 The magnetite is i-ather une\enly distributed, but, in the irregu- 

 larly bounded regions in which there is very little finely divided 

 magnetite, there Is a roughly proportional amount of large ragged 

 aggregates of magnetite, sometimes surrounded by calcite, and in 

 particular, the magnetite is aggregated into crevices and around 

 the vesicles as described from Macllveen's complex (6, p. GOO). 

 Associated with this same complex, is the quartz-bearnig kerato- 

 phyrc very poor in magnetite (No. 1113) tlescribed above. 



The Qaarlz-maynetite-kendophijres are of several types. The 

 most common is exemplified by specimens from the \\'ater 

 Reserve, betAveen Portions 51 and 52, by one (No. 1117) Irom 

 near the Jasper Knob in Portion 55, and by No. 1101 in Portions 

 35, 3G. All these rocks are vesicular, the vesicles being tilled 

 usually with (piartz and chalcedony, together with a little epidote 

 and occasionally felspar. Karely, they are filled with chlorite and 

 quartz. The groundmass of the rock consists of a spongy mass of 

 laths of acid i)lagioclase with interstitial quailz, dotted with 

 minute crystals of magnetite. The pheiuxnysts are albite some- 

 times undergoing" replacement by f|uartz, magnetite, rarely augite 

 (No. 1101). A fi-e(iuent feature occui-s around the margin of the 

 vesicles or in large irregular ci-acks. The spongy, texture of the 



