130 = Lieut. Baddeley on the geognosy 
distinguishes them. (turbinoliz ?*) All these fossils haye been 
probably washed up from the bottom of the lake, the island be- 
ing apparently a mere sand bank. There is another island near 
it which, judging from description, is probably composed of 
clay-slate. 
On leaving the former island we stretched across to the main, 
and entering a bay reached the mouth of the Ouitchouan, where 
another deposite of clay-slate was noticed. This slate differs 
from the other in the following particulars :—the strata are 
horizontal or nearly so—it is not observed to be here associa- 
ted with any other rock—its weathered surface is white, where- 
as that of the other is black.—it effervesces in acid very slight- 
ly, and contains slight traces of organic remains, neither of 
which characters was observed in the other—it is in greater 
abundance and more easily quarried. 
A person unacquainted with the deceptive appearances which 
rocks sometimes assume, would without hesitation pronounce 
this rock to be horizontally stratified, and in our judgment he 
would be correct ; but there are other surfaces which have a 
parallel arrangement among themselves, and which might easily 
be mistaken for planes of stratification, particularly as thei, 
position is vertical and one which agrees better with the high 
dip the clay-slates so generally exhibit. However upon a closer 
examination of these planes they are found to suffer constant 
interruption and not to be continuous. The horizontality of 
the strata being here assumed as the fact, of which we entertain 
no doubt, the laminz of the clay-slate are as before parallel to _ 
the surfaces of stratification. This rock is divided often, owing 
to 
* We have seen specimens from Drummond’s Island, Lake Huron, the 
structure of which is nearly as compact as ivory, owing to the infiltration 
of siliceous particles into the original interstices of the coral. ‘This, together 
with their yellowish white fractured surface, render the denticular resemblance 
atill more striking. 
