394 Review of the Progress of 
appears not improbable that future researches will enable us to 
divide this series of rocks into two or more distinct systems. 
Overlying the Laurentian series on Lake Huron and Superior, 
we have the Huronian system, about 10,000 feet in thickness, 
and consisting to a great extent of quartzites, often conglomer- 
ate, with limestones, peculiar slaty rocks, and great beds of dior- 
ite, which we are disposed to regard as altered sediments. These 
constitute the lower copper-bearing rocks of the Jake region, and 
the immense beds of iron ore at Marquette and other places on 
the south shore of Lake Superior have lately been found by Mr. 
Murray to belong to this series, which is entirely wanting along 
the farther eastern outcrop of the Laurentian system. This Hu- 
ronian series appears to be the equivalent of the Cambrian sand- 
stones and conglomerates described by Murchison, which form 
mountain masses along the western coast of Scotland, where 
they repose in detached portions upon the Laurentian series. 
_ Besides these systems of crystalline rocks, the latter of which 
that the gneissoid ranges in Eastern Canada have the form of 
synclinals, and are underlaid by shales which exhibit fossils in 
I'o this notion of the existence of two groups of crystalline 
rocks similar in lithological character but different in age, we 
