4-0 l-AKK SUI'KltlOll. 



for an invoati^ation of tlioir niiturn-l loiit.un>H; Rotno ninninfj; oaat and 

 wost, othci'H Htnii;^lit north a,n(l Hoiitli, iind oiluu'H Jorniin;!; a n^^iilar 

 ci'CHcont'., witli its convoxity tinMiod nortlivvanlH. TIkmi' absolute jx)- 

 silioii is ;iJ. oncti cliiuiu'tcristic, TlKiy ivro oxcavatod chieHy between 

 the |)Iu((»iii(i iii!iss(\s risiu;;; north, mihI th(> strutiruHl d(>])osits Bouth of 

 the |iriiiii(iv(! rMn;!;(>. 



lj;ilio Superior, cspcciMJly, lills m, chMSiu between the northern 

 ;i;rani(i(! and nu'tMuiorphic r;in,i:;<', and tho ohh'st b(Mls ih^posited 

 alou'j; tli(>ir soul hern slopes in th(^ |triniitiv(> !i,l!;o of tliis (Continent. 

 Ijiike ()iit;nio iuid Lnle I'lrie, on llie conlrMi'v, run between th(> suc- 

 cessive hiyors ol" dilVerent setsoC bods of tho same ^rciit ^co;j;r;>|)hical 

 period; whihi liid^es IIin-ouMnd Miehii;Mn (ill )ip tli(> (U'Mcks which 

 run at i'iii;ht ati!j;les with iJie ni;iin northern priniilivt^ r:tii;;t>, :uid 

 wliieh, no (loui>t., ow(> tht'ir oni:;iu to the eievaiiou ol' th(> chains north 

 of halve Huron and JjaJu; Su|>(>rior ; repeatini;-, on a lar^c^ S(;alo, 

 what has been said above of the (l(>pendence of the Swiss lakes 

 upon tJH'ir L:;eoloL';ieal positions and relation to Ihi^ mountain ciiains 

 which eneirch^ them. 



Besides this ;j;eu(U"a.l ndation of the lakes in couneetion with their 

 shores, I ha.V(> been able to trace a. more uilunat(> counecliou of the 

 outlines ol" their shores and tlii-ir ;^(>oloi;ical strnctui'c, (>sp(>ciallv in 

 |jak(» Supei'ior. 



As a whol(>,tliat lake r(>S(Mubles a. larii;e crescent, with its convexity 

 turned northwards; but it wcvc a, ^real mistake to imagine that this 

 foi'in is actuallv thc^ I'orui of tlu^ shores, or that, it is iv^pi^atcd upon 

 (>\('i'v point. On the coulrary, the ij;(>ueral outline of that, lakc^ is 

 tlu> accidental result ol" the combination of many details, of many 

 <:;eolo;!;ical ev(>nts which have I"o11ow(mI (>ach other at dilfcrent jjoriods,- 

 hav(> modified the tract of land where th(> Inko now exists, ivnd liavo 

 cut up its l"oundation in such a^ mannei' as to break the continuil\' of 

 l;h(^ solid rock, and allow it to be decomposed. Thus an (Jxtcnsivo 

 erescent-sha])cd iiole with inn(nu(>rable islands lias been fornuMl, in 

 which the islands, in their various bearings, still indicate* the direction 

 oi" (h(> intcrscctin;:; masses, and appear at pr(\sent as tlu> frai^meutary 

 remains o[' u eontinuous tract of land, which is now ri-phuu'd by a 

 d«>ep lake. 



for many weeks 1 had been tracin;:; tlu> dvkt.>s which intersect the 



