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 Colher's Harbour. A description 

 of the organic remains of the Manitoulines (as far as they 

 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 

 their fantastic shapes and luxuriant shrubbery, and the short 

 sides, pebbled beaches. 



The 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 

 crystaUizations. The size of the fragments varies from one 

 to eight inches. They also are of an ochiy yellow. The 

 bottom of the cliff is in horizontal strata, which are mode- 

 rately thick, very soft, even so as to write, and of a white, 

 or bluish colour. I have been thus minute, on this spot as 

 the herbage does not permit an examination at any other 

 except in small patches where similar appearances were no- 

 ticed. 



The north-west half of this long side of the Island de- 

 clines in height very gradually and consists of debris except- 

 ing a few schistose strata at the top. Not far from the end 

 a road is making up the steep (1819.) Here the limestone 

 contains a few blue and white striped flints, which are re- 

 markable for being broken, small, and angular. They are 

 also met with on the beach. I met with no organic remains. 

 A friend saw a single bivalve. There are indeed several 

 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. 



