322 APPENDIX. 



Dear the entrance of the Brule, or Misakoda Kiver, as seen in the 

 illustration beneath. Shores of sand then intercept its view to 

 the entrance of the Eiver St. Louis, and up its channel to its first 

 rapids, about eighteen miles, where the red sandstone again 

 appears, as the first series of the Cabotian Mountains, 



Serpentine Eock. — At the nearest point north of Eivier du 

 Mort is a headland of this rock, jutting out from the granitical 

 formation. Lapping against it, at the mouth of the river, is a 

 curious formation of magnesian breccia. The serpentine rock 

 appears, in nearly every locality examined, to be highly charged 

 with particles of chromate of iron. It may be expected to yield 

 the usual magnesian minerals.* Its position is between the Carp 

 Eiver and Granite Point, in the Bay of Presque Isle, or rather 

 Chocolate Eiver, for that river pours into this bay by far the 

 largest quantity of water.f 



Ancient Drift-Stratum. — In the intervals between the points 

 and headlands, where the rock formation is exposed by streams 

 or gorges, the drift, or erratic boulder stratum, is found. Such 

 is its position beneath the sand-dunes of the Grandes Sables, and 

 in the elder plains and uplands, stretching with interruptions on 

 the coast from the head of the Mary's valley to that of the St. 

 Louis. The edge of this formation is composed of the sand and 

 loose pebbles and boulders of the lake. Mighty as are the exist- 

 ing causes of action of the lake in beating down and disrupting 

 strata of every kind, and in reproducing alluvial lands and dunes, 

 they are weak and local when compared to the causes which have 

 spread these ponderous boulders, and drift masses over latitudes 

 and longitudes which appear to be limited only by the leading 

 elevations of the continent. That oceanic torrents of water, sud- 

 denly heaped on the land, and wedged into compactness and 

 power now iinknown to it, is after all, the most plausible theory 

 of the dispersion of this formation, and this theory avoids the 

 necessary local one of the glacial dispersion which presupposes a 

 very low temperature over the whole surface of the globe. 



* In 1831, in making some explorations of this rock with gunpowder, I found the 

 serpentine in a crystalline state, of a beautiful deep-green color, but appearing as 

 if the crystallization was pseudoraorphous. 



f The extensive iron mines of Marquette Coiuity, Upper Michigan, are now 

 worked in this vicinity. 



