66 NAREATIVE OF THE EXPEDITION. 



on the surface, along witli fragments of breccia, quartz, &c. This 

 drift is more abundant, on all the islands I have seen, as we 

 approach the north shores of Lake Huron, Having completed 

 the examination of these islands, we returned to the harbor after 

 an agreeable excursion. 



To observe the structure and character of the Island of Michili- 

 mackinac, I determined to walk entirely around it, following the 

 beach at the foot of the cliffs. This, although a difficult task, 

 from brush and debris, became a practicable one, except on the 

 north and northwest borders, where there was, for limited spaces, 

 no margin of debris, at which points it became necessary to wade 

 in the water at the base of low precipitous rocks. In addition 

 to the reticulated masses of limestone covered with calcspar from 

 the fallen cliffs, the search disclosed small tabular pieces of mi- 

 nutely crystallized quartz and angular masses of a kind of striped 

 hornstone, gray and lead colored, which had been liberated from 

 similar positions in the cliffs. On passing the west margin of the 

 island, I observed a bed of a species of light-blue clay, which is 

 stated to part with its coloring matter in baking it, becoming 

 white. 



While the British possessed the island, they attempted to pro- 

 cure water by digging two wells at the site of Fort George (now 

 Holmes), but were induced to relinquish the work without success, 

 at the depth of about one hundred feet. Among the fragments 

 of rock thrown out, are impressions of bivalve and univalve 

 shells, with an impression resembling the head of a trilobite. 

 These are generally in the condition of chalcedony, covered with 

 very minute crystals of quartz. I also discovered a drift speci- 

 men of brown oxide of iron, on the north quarter. This sketch 

 embraces all that is important in its mineralogical character. 



This island appears to have been occupied by the Indians, 

 from an early period. Human bones have been discovered at 

 more than one point, in the cavernous structure of the island ; 

 but no place has been so much celebrated for disclosures of this 

 kind, as the Skull Cave. This cave has a prominent entrance, 

 shaded by a few trees, and appears to have been once devoted to 

 the offices of a charnel-house by the Indians. It is not mentioned 

 at all, however, by writers, till 1763, in the month of June of 

 which year the fort of old Mackinac on the peninsula, was trea- 



