268 Geology and Mineralogy of the 
Masses of honeycomb and chain madrepores are frequently 
met with two or three yards in diameter ; but the material 
of which they are composed being more calcareous they are 
not so beautiful as those at Collier’s Harbour. A description 
of the organic remains of the Manitoulines (as far as the 
have been examined) will be found in the Appendix. 
The island of Michilimackinac, (situated close to the 
straight dividing Lakes Michigan and Huron; and in the 
latter) is of an oval form and nine miles in diameter; the 
long sides being lofty precipices rendered picturesque by 
ir fantastic shapes and luxuriant shrubbery, and the short 
sides, pebbled beaches. 
e rocks are calcareous; and the clear idea of their na- 
ture is afforded by the south-east extremity of the north- 
east precipice which may be described as follows :—A few 
soft strata, very thin, white and horizontal, shew themselves 
at the top; but below this the limestone becomes yellow 
and ragged. Much of it is compact, but it is more usually 
occupied by vesicles (as from bubbles of air) encrusted with 
crystals of quartz in botryoidal clusters. A few of them are 
three or four feet in diameter, and contain smaller cavities 
in several series. Other parts contiguous to this, are an ag- 
gregate of angular fragments of slaty limestone cemented 
as if by semifusion, and with interstices lined with quartzose 
erystallizations. The size of the fragments varies from one 
‘The north-west half of this long side of the Island de- 
clines in height very gradually and consists of debris except- 
A friend 
fragments of the limestone of the Lesser Manitou on the 
shore, penetrated by a multitude of short incisions as with 
the point of a knife, 
