of Lake Superior. 233 



compact. This great stratum of conglomerate has no subdivisions, 

 but has frequently a partial layer, (one foot thick, with ragged, 

 thinned, edges) a few yards square only, of this sandstone, coarse, 

 or very fine, and even resembling baked clay. This conglomerate 

 is cemented by the finer fragments of the rocks forming the 

 nodules, often so small as only to be discerned by careful exami- 

 nation. The nodules are rounded and lie promiscuously, usually 

 set very fast, the outer ones not loosening readily on exposure to 

 the air. The largest are 30 lb. in vireight, the smallest are invisible; 

 the average weight being from a quarter of a pound to a pound and 

 an half; I saw one, however, which might weigh lOOlbs. They 

 consist of various greenstones, pale granular, and red porphyritic 

 granites, numerous translucent white, and brown granular, quartzes, 

 the former having a bright red tint around the outside only. The 

 majority of these nodules, however, are the different species of 

 amygdaloids and dense ferruginous sandstones, Masses of green 

 earth are not uncommon. Most of them have a thin envelope of 

 this substance, of calcspar, or of iron-rust, sometimes indeed of 

 all the three. White rhombic calcspar occurs in this pudding- 

 stone in nests and veins from one to four inches thick, traversing 

 it in all directions. In two instances I saw a vein of calcspar, a 

 quarter of an inch thick, pass successively through a nodule of 

 greenstone, granular quartz, and an amygdaloid. 



Three miles or more below Point Marmoaze, the waves have 

 laid bare two patches of conglomerate, conformable to the trap, 

 but rather resembling the sandstone of Batchewine than the pud- 

 dingstone of Point Marmoaze. The one is «laty, dark brown, 

 and of fine texture, nodules obscure ; the other is very coarse, 

 and consists of fine sandstone nodules, red and white, with masses 

 of green earth, calcspar, 4^c. 



The veins in the amygdaloid are numerous. They are as fol- 

 lows : — A dense clay iron-stone ^ — 1 inch thick, vertical, running 

 in all directions, and ramifying at acute angles. 2. Satin spar, 

 white, (having rarely a tinge of red,) in veins from a quarter of an 

 incii to an inch thick ; vertical, running obliquely to the strati- 

 fication, several veins in company, nearly parallel, and sending off 



Vol. XVIII. R 



