62 Copper Mines. [Jan., 



strong reason for believing that the mineral region of Lake Su- 

 perior will prove an exceeding rich one.* 



In addition to these rocks there occur reposing upon them un- 

 conformably those belonging to the sedimentary class, which con- 

 sist lithologically of cemented quartz, trap and greenstone, form- 

 ing a singular conglomerate. This is the lowest mass; and, in 

 tracing it upwards, it passes into a red or brown sandstone, mot- 

 tled in many places with green : it is also traversed extensively 

 with quartz seams which often branch out like the roots of a tree, 

 or else form a net work of the same material. This arrangement 

 imparts a singular aspect to the cliiffs when they are exposed upon 

 the shores. Of the conglomerate and the sandstone, into which 

 it passes, there are innumerable varieties, differing from each, 

 other: some in color, some in hardness, and others still, in the ar- 

 rangement of the elements which compose them. 



Dr. Eights, in his communications, makes a distinction between 

 this conglomerate beneath the sandstone and another which he 

 styles a trap tuff, which is clearly of a recent origin, being really 

 a consolidated diluvium, w^hich consolidation, instead of being 

 produced by infiltration of the carbonate of lime, is really a baked 

 mass, or consolidation effected in later times, by igneous, rather 

 than by aqueous action. 



*It is proper to say to those of our readers who are not familiar with 

 the names and characters of rocks, that trap, amygdaloid and basalt are 

 rocks of igneous origin ; they are, in other words, ancient lavas which were 

 poured forth in a molten state, from below, while the surface of the country 

 was covered with water. Hence they appear as filling fissures or wide 

 cracks, and frequently they appear to have overflowed the parts adjacent to 

 these cracks, which, when filled, are called dykes. These rocks have been 

 formed at all periods, and hence may rest upon and cut through any sedi- 

 mentary rock of any age. They frequently bring with them to the surface 

 the metals in the form of sulphurets, oxides, native or alloys. The amygda- 

 loid resembles most frequently a recent lava, only the pores, or vesicles, are 

 Generally filled with spar, or some mineral substance which has infiltrated 

 into them since the period of their formation : what is called greenstone, is 

 far less vesicular, and basalt is perfectly compact ; they have the same origin, 

 bat were subjected to pressure at the time of their ejection, and hence the 

 vesicular structure is wanting. 



