118 Feather stonhangh''s Geological Report, 



rated afterwards, and proved to be the same species as others 

 now found in the neighboring parts of the lake. The next 

 two hundred and thirty-five miles, to the island of Michili- 

 mackinac, I made on the lake.* This is a small island, formed 

 of a soft and extremely porous calcareous rock, broken down 

 from top to bottom into a breccia, and re-cemented. It has at 

 some period been much higher than it is, isolated portions 

 still remaining far above the general level. The Sugar-loaf, 

 a sort of pinnacle, or out-lier, is an instance of this. It is a 

 brecciated pillar, composed of adhesive portions of the old cal- 

 careous beds, which have resisted the causes that have over- 

 thrown the stratification ; some of the masses are vertical, 

 others highly inclined, and some horizontal. In some parts 

 of the island the beds were not so much disturbed, and were 

 underlain by soft, marly, broken-down, calcareous matter. I 

 saw very heavy masses of the same porous limestone which 

 had been fished up in the bay, which proves that the island 

 is an out-lier, greatly reduced in size, of what was once con- 

 nected with the adjacent country. This my time did not per- 

 mit me to visit. There is not much to occupy a geologist on this 

 island, but in my walks to a small plantation called the Farm 

 of the Mission, I saw an extensive lacustrine deposite, full of 

 various species of planorbis, &c. of the usual kind, the which, 



* It appeared to me somewhat remarkable that on this already important line 

 of navigation to Michilimackinac and the Wisconsin Territory, frequented 

 by the craft of the country and by steamboats of the largest burden, the maps 

 should be so absurdly erroneous as, they are, as to the distances. In tliose 

 which T had, and I believed myself to have tiie best, Presqu'isle is put down a 

 great deal too near to Michilimackinac, and Middle island occupies the place 

 where Thunder island ought to be. The following table of distances was cor- 

 rected for me by an experienced navigator on this lake : 



Fort Gratiot to Point aux Barques - - . - 70 miles, 



to Thunder island - - - - 70 



to Middle island - - - - - 12 



to Presqu'isle - - - - - 18 



to Bois Blanc, called Bobbelo - - - 55 



to Michihmackinac - - - - 10 



