252 0?i the Geography and Geology 



held in certain lights. It effervesces moderately in acids ; and 

 is very slaty, and weathers readily. It is generally horizontal. 

 At the north angle of the most easterly large island of the Pay 

 Plat, the layers undulate in small sets ; these sets, however, 

 being, by no means, parallel to each other; often, indeed, straight 

 and horizontal. Lieutenant Bayfield favoured me with a sketch 

 representing sandstone and conglomerate incumbent on amygda- 

 loid, in the sides of a narrow entrance to a cove in an island in the 

 Mammelles, fourteen miles east of Thunder Head. The sandstone 

 is here stratified in gentle curves, concave towards the amygdaloid, 

 on which it is placed. Most commonly the sandstone is detached 

 from other rocks ; and is surrounded by woods. 



The puddingstones which accompany this sandstone vary : — in 

 some cases the cement is sandstone ; but generally near inspection 

 proves it to be greatly comminuted fragments of the rocks consti- 

 tuting the larger nodules. White calcspar is often present among 

 the cement ; sometimes in very great quantity. There is often 

 green earth. The nodules are very numerous and diversified. 

 They are not so much worn as in every case to have lost their 

 angles. They consist of the amygdaloids and porphyries of the 

 district, especially of the latter, only having small masses of 

 limpid quartz, of red granite, like that ten miles west of the 

 Otter's Head, pale and dark greenstones, translucent crystalline 

 and opaque granular quartz, sandstones, and jasper. The size 

 of these nodules, and the aspect of the conglomerate, en masse, is 

 the same as at Marmoaze. 



This conglomerate, according to my experience, is confined to 

 the north side of the Nipigon islands. I have only seen it rising out 

 of the water solitarily in low and shattered amorphous patches ; but 

 Lieutenant Bayfield has observed it overlying white and red sand- 

 stone, incumbent on amygdaloid ; while Major Delafield has met 

 with it between amygdaloid and sandstone. 



The amygdaloid of the Pay Plat and Mammelles differs from 

 that of the east coast of the lake only in being less ferruginous, 

 and in the occasionally darker tinge of its green earth. The im- 

 bedded substances are in smaller proportion. In fact, the amyg- 



