Lake and River Temperatures. 15 
their outlet to Lake Huron through the River St. Mary. 
The island of St. Joseph divides the river, as it joins Lake 
Huron, into two channels, one of which transmits its waters 
partly through the Detour into the Central Basin of the 
lake, and partly into what might be termed the Manitoulin 
Basin, on the north side of the Manitoulin Islands, whilst 
the other channel guides its waters entirely into this latter 
basin. It at once suggests itself that the waters of this 
Manitoulin Basin must be cold, and that the flow of these 
colder waters, whilst in part to the Central Basin of Lake 
Huron by the channels between the islands, is more prob- 
ably largely along the north side of these islands and into 
the Georgian Bay, thus continuously keeping up the supply 
of cold water, which is so conspicuous a feature in that bay. 
Commander Boulton’s records seem to me to help this sug- 
gestion. Thus,in the Manitoulin Basin, north of Cockburn 
Island, on June 3rd, 1890, at 10.30 a.m., with a cloudy sky 
and the air at 54°, the surface water indicated 44.7°, whilst 
the temperature at 29 fathoms was 39°; and, again, at an- 
other point nearer Cockburn Island, at 8.30 a.m., on the 
next day, when the sky was clear and the air at 66°, the 
surface of the water was 46.5°, whilst the bottom at 18 
fathoms indicated 39.7°. 
Again, the preponderating current in the channel between 
La Cloche Island and the north shore of Manitoulin Island, 
at the point known as Little Current, is, Commander Boul- 
ton informs me, towards the Georgian Bay. As an easterly 
wind may reverse its direction for the time, he suggests 
that the easterly current might be merely surface-drift, due 
to the prevalence of westerly winds. My own impression 
is that it will be found to be a permanent, deep current, 
flowing towards the Georgian Bay. 
It is, however, also suggestive that the cold waters from 
Lake Superior which do pass through the Detour, and the 
channels between the Manitoulin Islands into the Central 
Basin of Lake Huron, are not immediately incorporated 
with the warmer Michigan outflow, but trend in an easterly 
and south-easterly direction towards the Georgian Bay and 
