314 . APPENDIX. 



soil, both of the fibrous and compact variety. These islands are 

 low diluvial formations. Similar masses are found on Goose 

 Island ; and the mineral has been found at Point St. Ignace on 

 the main land. 



Taken in connection with the discovery of this mineral, at a 

 subsequent part of the journey on Grand Eiver, the indications 

 of the series of the saline group of rocks, so prevalent in the 

 Mississippi Valley, are quite clear up to this extreme point, which 

 is, however, very near the northern verge of this group. 



Honeycombed Rocks. — As evidences of existing lake action, 

 it has already been mentioned that the fishermen bring up, from 

 great depths in the straits, pieces of compact limestone, com- 

 pletely fretted and excavated by small pebbles, which are kept 

 in motion by the strong currents which prevail at profound 

 depths. The process of their formation by these currents is 

 such, as in some instances to give the appearance of cellepores, 

 and analogous forms of organic life. I have seen nothing in 

 these carious forms which does not reveal the mechanical action 

 of these w^aters. 



PsEUDOMORPHic FoRMS. — Amongst the limestone debris, of 

 recent date, found on these shores, are pieces of rock which have 

 an appearance as if they had been punctured with a lancet, or 

 blade of a penknife. These incisions are numerous, and from 

 their regularity, appear to have been moulded on some crystals 

 which have subsequently decayed. Yet, there are difiiculties in 

 supposing such to have been the origin of these small angular 

 orifices. 



Whenever these masses are examined by obtaining a fresh 

 fracture, they are found to consist of the compact gray and semi- 

 granular rock of the inferior Mackinac group, but in no instance 

 of the vesicular or silicious varieties. These blocks appear to be 

 identical in character with the White Rock, before noticed. 



North Shore of Lake Hurox. — The next portion of the 

 country examined was that of the north shores of the lake, ex- 

 tending from Michilimackinac to Point Detoiir, the west Cape of 

 the Straits of St. Mary's, a distance computed to be forty miles. 

 The calcareous rock, such as it appears in the inferior stratum of 

 Mackinac, extends along this coast. The first three leagues of it, 

 consist of an open traverse across an arm of the lake. Goose 



