JV. W. Portion of Lake Huron. 26 1 



splintery ; so much so that the precipice frequently changes 

 into a steep dechvity of schistose debris. At the head of 

 the narrows the greenstone is much less disintegrated, and 

 dips into the clear and deep waters in compact walls of al^ 

 most pure hornblende. The contiguous islets (filling up the 

 interval of a mile between St Joseph and the main,) are of 

 a similar formation, and are composed of aggregated ridges, 

 rising to a great height, and presenting to the current rapid 

 slopes of smooth rocks or perpendicular cliiFs.* 



The head of the narrows being the seat of a strong cur- 

 rent, is one of the north west limits of Lake Huron. Ad- 

 vancing still north westward we come to the lower of the 

 two basins (included between the north main and St. Jo- 

 seph) which separate Lake Huron from Lake George on 

 this side. The shores of the lower basin being marshy or 

 alluvial, as is to be expected at the entrance of so confined 

 a pass as that of the narrows, no strata are met with as far 

 as I am aware, until we arrive at the rapid formed by the 

 line of islets, dividing the lower from the upper basin. Here 

 a new order of rocks occurs. 



It is of quart'z and is of the transition class, as appears 

 from its associations, its inclination and the breccias and 

 nodules which it frequently contains. It prevails from hence 

 to Lake George, (five and a half miles.) Its direction is 

 distinctly north west, with a dip either vertical or obscure ; 

 but at the islets of Encampment Douce, at the foot of the 

 rapids of the Great Nibish, this is perhaps not quite so evi- 

 dent from the innumerable rents and dislocations, and from 

 original displacements. 



On the third large island from the rapid of the basins, 

 (above mentioned) a parallel stratum of almost sienitic 

 greenstone occurs, and the same is seen on the main three 

 miles north north west. It may be a continuation of the 

 stratum of the rapids. 



The composition of this quartz rock varies much. It is 

 here an aggregation of minute grains of vitreous quartz ce^ 

 mented by the same substance, opaque and of a milky white 

 colour. It is easily frangible, and becomes soft and pow- 

 dery on exposure to the weather : the external surface how- 

 ever is frequently hard and smooth in patches. Its frac- 



* Dir. N. W. dip. vertical. 



