ISO EXPEDITION TO THE 



to them any but an immense cause. By those who object 

 to the igneous or volcanic theory of the formation of trap 

 rocks it will perhaps be argued, that the immense extent 

 of country, on the shores of Lake Superior, which is co- 

 vered with these rocks, opposes the belief of their being the 

 product of volcanoes ; but the same has been said of the se- 

 condary trap formation of Bohemia, Auvergne, &c. While 

 the igneous origin of these is supported by the respectable 

 names of Uesmarais, Humboldt, Von Buch, D'Aubuisson. 

 &c. we may, arguing from the sound principle, that like 

 effects may in both hemispheres be traced to similar causes, 

 be permitted to consider the trap rocks, which we observ- 

 ed, as being probably of a volcanic origin. 



We are not aware that the spot which we visited has 

 ever been examined by any geologists, except by Dr. Bigsby 

 and Major Delafield. With the former of these gentlemen 

 we met at the Sault de St. Marie, after our observations on 

 these rocks had been completed ; if he has published his 

 views on the subject we have not yet seen them. We have 

 not seen Major Delafield, nor do we know of any publica- 

 tion of his upon this subject, so that the above observations 

 are offered rather with a view to call the attention of future 

 travellers to this interesting question, than from any wish 

 on our part to express a decided opinion upon a subject 

 which, in the present state of our acquaintance with that 

 country, we freely confess to be beyond our reach. 



These amygdaloidal rocks, interspersed with other va- 

 rieties of trap rocks, were frequently seen on the coast of 

 the lake. We, however, often saw also sienite, but never 

 had an opportunity of examining the junction of the two 

 rocks. On the morning of the 17th, we observed a beau- 

 tiful red porphyry, which on inspection we found to be 

 formed by fine crystals of feldspar, united by a cement of 



