Postelsia 303 
appearance, and many of the causes of forma- 
tion are the same. 
The principle difference in the cause of 
formation is the effect of tides on the pools 
along the coast. Further, it is supposed that 
the potholes, or kettle holes, as they are some- 
times called, are caused by glacial action. In 
the pools studied on the Vancouver coast, it 
does not seem probable that the formation of 
the pools has in any way been determined by 
glacial action. 
The following articles give discussions on the 
subject: 
Manning, P. C. Glacial potholes in Maine. 
Proc. Portland Society of Natural History. 
Kjerulf. Potholes. Description of giant kettles 
in Norway. 
Tarr. Physical Geography of New York State. 
Geike. Scenery of Scotland. 
Description of Plates. 
Plate XX. t. Sculpturing of shore cliffs. 
2. Cliffs with seaward platform. 
