202 Dr. BiGSBY on the Geography and Geology of Luke Huron. 



by the Commissioners under the Treaty of Ghent, to the United States, the 

 British garrison will be withdrawn ; and as it will not be held as a military 

 post by its present owners, it will be long, probably, ere its fossils again be- 

 come the object of research. 



The first of the organic remains which I shall describe, are some corals 

 found in the quartzose limestone at Collier's Harbour, and at the west end of 

 the Grand Manitou, differing from any that have yet been discovered in a 

 recent or fossil state. Their variations of external form are such as to have 

 led me to separate them into five species ; and as it is in that particular alone 

 that they differ, it is of one only, and that the most abundant, that I have given 

 a detailed description ; contenting myself, as to the rest, with pointing out 

 those changes of form which distinguish one species from another. The figures 

 are all of the natural size. 



Species I. — The corals of the species represented in Plate XXVIII. fig. 2, 

 have in their general appearance a considerable resemblance to vertebrae. 

 They are columns, tapering from the top, composed of similarly formed joints, 

 which diminish downwards both in length and breadth, though not in regular 

 gradation. The length of each joint in this species is about an inch, and the 

 breadth exceeds the length. The transverse section is circular. The lower 

 and middle part of each joint is cylindrical, or slightly conical; the upper part 

 swells out, and is inflected inwards at the top, so as to meet entirely the base 

 of the joint next above it. This dilated part is, in different species, in very 

 variable proportion to the rest of the joint. The lower part of one joint is in- 

 serted, to some little depth, into the upper part of that next beneath it, so as 

 to attach the joints firmly to one another. The external surface is covered 

 over with a thin smooth coat ; but this is rarely preserved, and then only in 

 small portions. The surface is usually without this coat, and is then longitudi- 

 nally striated. 



Where the joint is most dilated, a thin horizontal septum, formed by the 

 abrupt inflexion inwards, and coalescence of the upper and lower parts of the 

 outer coat, passes transversely across the joint ; as is seen in two of the joints 

 in figure 2. 



The section represented in fig. 6 shows the radiating lamellae peculiar to 

 madreporae, and the congenerous lamelliferous corals. These lamellae are lon- 

 gitudinally disposed, and radiating from the axis of the column to its parietes, 

 there form the external striae. 



In the axis of the column is a hollow tube ; but the whole interior of the 

 column is in most specimens obliterated, being filled with dark granular lime- 



