OUTLFMOS OF LAKK BUI'KIUOU. 421 



sliorofl of Tifiko Su[)orior in ulinost all (lir(!(;iioMM,\vlH)n I was onn day 

 nioHfc lorciljly Htnick wiUi i\m I'jict, Uuih Uicmo dykoH ii'^rci^, in tlioir 

 bcaringH, ■with tho boarin^^H of IIm! nliorcH ; jukI tlial, (ivnti tlio ;^r<!at,()Ht 

 complicaUotiH iti Uio onUinos of tJic, Hlion;,-( cduM lio accouiiUMl for, by 

 til'! C(>rnt)iri;i,t,ioiin ol" (lyk<!H itil,(5rHc(;t,iri^ ('.',i(;\\ fdJior in diU'c-niiit, dircc- 

 tioTiH. And ind(!(!d, now llial, I liiivo IJk: k(!y ("or iuirli ;ui JuiidyHiH, 

 I find no dillicnlty in rof'orrin^, oven Hborb linoH ol" Uic coaHl,, to 

 the dillorcrit HyHtcms of" dykcH whi(;b I know to cxiHt tlicro, and 

 wbcrover my memoranda are Hnlli(;i<rit,ly lull, I lioil indieatioiiH of 

 dykoH rnnnin;^ in tlif; direction of the eoiiHt. Ah Hoon aH my attention 

 had been ealled to tlieno phenomena, I. iont no opf)ortunity ol' invest- 

 i;^atin;j; tho nature of tho rock of tlioHe dilierent nyHt(!mH of dykes, 

 and 1 ascertained, to my groat astonishment, that there are consid- 

 er.'i})le diirerenees in their mineraloj^iea! characters ; some beiri;.'; am- 

 f)hiliolic tra|) ; others bein;^ inj'-etfid with (![)idote ; otlnirs having 

 moie tlif; ;ip|)c;i.r;uiee of pit.eliHtone ; ;i,nd, what is parlieida,rly inter- 

 (jstin;.';, tlx; dykes which nni in the sajrie direction |)res<!rv<; the same 

 mineralo;^ical character, as well as the namc! bearinn;. 



'J'hc systems of dykes which run <lir(;f;tly north and Honth, and 

 ■which form the inlets hetw<;en Nef!f)i;^f»n l»ay and the ma,in lake,a,nd 

 int'-i'sect the lar;//; ishmd of St. I;jrnace, and H(!para,t(! St. Jgnaco 

 t/5'iticlf fr-om the main land, a,ll rnn north a,nd south, and consist of 

 very hard, ton;^h, unalterable liornbhinde trafi, of a crystalline 

 aspfct, and a grayish color ; while tlie dykes, which run east and 

 ■west, and mark out tlie northern and southern shorcH of those Hamo 

 islands, consist mostly of a greenish trap extensively injected with 

 cpidote, and breaking with tJie greatest ease into angular, iiregular 

 fragments. 'J'he nf>rthern shore east of tlie Pic has the same general 

 bearing, duo oast and west ; and here, also, we lind the dykes moro 

 or less e[)idotic, and the metamorphic rocks talcose. 



Again, the long shore running due east a,nd west from iVJifdiifiicf)- 

 tin westwards, is, also, along its whole extent, intersected by epidotic 

 dyl.<!S runnirig east and west. 



'I he dykes of tin; north-eastern coast of the lake between the I'ic 

 and Michif)ieotin Island, which nm north north-east to south south- 

 west,, consist ()\' a [)itch,Hton(; traf», lik<! black glass, whifdi, notwith- 

 Btiinding its external hardness, readily decomposes, and i'orms almost 



