N. W. Portion of Lake Huron. 263 
It may be conjectured that these two rocks owe their ori- 
gin to the trap and granite on the north east, or that they 
have been evolved from the same repository but in closer 
combination, 
The Huttonian theory explains these phenomena, by pro- 
viding powers and materials. cagteaie” 
urther evidences of the convulsions to which this part 
of Lake Huron has been submitted, are afforded by the six 
distinct species of conglomerate in the state of debris, and 
as many of breccia which every where abound ;* and by the 
brecciated and vesicular limestones of Michilimackinac. 
Most probably the first fletz sandstone is the rock in jux~ 
ta position on the north west, with the transition quartz 
just described. PE a ge eee os 
* Jt have not visited in favorable circumstances the line of 
junction, and I saw the former first distinctly at the falls of St. 
Mary, among the petty rapids of the marshy islets around 
the falls. In the summer of 1819, while travelling in a ca- 
clets. It is the sandstone of the . 
without so large an impregnation of irom. 
2 . i : 
No fixed stratum, I believe. 
of St. Joseph, or ia the 
