IXTEEESTING LOCALITIES OF MESNAIM) (.U'AKTZITE. 235 



with (|Uart:cite.s, sonietinirs strouiily and coarsely fcldspatliic Tliuse pass 

 into tliL' pure quartzite^^ wliicli constitute tlie greater part of tlie bluff. 



\Vlieu this conglonierato was first examined it was thought that it 

 marked an unconformity, but a closer examination shows it to be iuter- 

 stratitied conformably with the slates and graywackes below, and Avith the 

 graywackes and quartzites above. Those below are precisely similar to 

 the slates and graywackes south of the State road north of Mud Lake, 

 and ajiparentlv are at the same horizon. In the upward gradation fi'om 

 this to the quartzite it appears that the currents were strong enough to 

 locally form a lied of conglomerate. The conglomerate differs from that 

 at the base of the series north of Mud Lake in the absence of abundant 

 granite and green-schist pebbles and in the presence of the varieties \vhicli 

 have been given as characteristic of it. The conglomerate appears to fol- 

 low along the Ijorder <if the hill to the east, and in field relations appar- 

 ently cuts slightly across the direction of stratihcatiou of the <iverlying 

 slates and quartzites, although no actual discordance was seen at any 

 localitw The juncti.>n of this conglomerate layer with the underlying 

 slates and gra}-wackes was a zone of maxinuim differential movement at 

 the time of the folding. As evidence of this, the slates are broken into 

 thin plates; they are heavily impregnated with oxide of iron; the con- 

 glomerate itself in certain places takes on a brecciated form, and its matrix, 

 as well as some of the ))ebbles, is lieavily im})regnated with iron oxide. 

 The gravwacke peljliles contained in the lowei" part of the conglomerate 

 probably have the same origin as those in the slates north of Mud Lake; 

 that is, thev are of dynamic origin. At various places the whole series is 

 cut through ])\' (habase dikes. 



A microscopical examination of the Omimi conglomerate shows that 

 the majority of the heavily ferruginous pebbles are decaying fragments 

 of a schistose rock, which have been strongly inq)regnated by iron oxide, 

 as has also the matrix. None of the quartzite-like pebbles are certainly 

 fragmental, although some of them at first sight have a clastic ajipearance; 

 but none of the grains show cores or enlargements, and they interlock. 

 They appear to differ from the cherts only in that the (quartz is more 

 coarsely crystalline. Some of these complex quartz pebbles are mashed 



