656 The American Naturalist. [July, 
General Notes. 
GEOLOGY AND PALEONTOLOGY. 
The Norian Rocks of Canada.—Professor F. D. Adams of 
McGill College, Canada has published a memoir on the Norian or 
Upper Laurentian rocks of Canada! This memoir is the result of five 
seasons’ field-work conducted for the Geological Survey of Canada, 
supplemented by a laboratory investigation of the rocks constituting 
‘the Norian series. According to Professur Lawson, two important 
results of Mr. Adams’ work are first, the clear recognition, as plutonic 
eruptive formations, of rock masses, which, being petrographically and 
geolographically units, have each an enormous extent. These are the 
Norian mass, which occupies nearly 1000 square miles; and the 
Saguenay mass, which is about six times that area. These masses, 
which may be termed batholites, are characterized by a distinct type of 
rock known as anorthorite. 
The second important result is the immense simplification effected in 
Archaean geology in the Canadian territory. (Science, May, 1893.) 
The Caudal Fin of Ichthyosaurian Reptiles.—In discussing 
the recent advances in knowledge of the Ichthyosaurian reptiles, Mr. 
R. Lydekker refers as follows to an important paleontological dis- 
covery which confirms Sir Richard Owen's conclusions that the 
Ichthyosauri possessed a caudal fin. 
“ From the circumstance that nearly all their skeletons found in the 
English Lias have a dislocation in the vertebre of the tail, Sir Richard 
Owen was led many years ago to the conclusion that the Ichthysaurs 
were furnished with an expanded fin at the end of the tail, and that 
the weight of this fin caused the fracture in question. In the present 
year, there has been discovered in the Lias one of these reptiles, in 
which the outline of the fleshy parts is completely preserved, and which 
proves the existence of a caudal fin of still larger dimensions than Owen 
supposed to be the case. This interesting specimen is described by Dr. 
Fraas (Neue Jahrbuch f. Mineralogie, 1892, pp. 87-90). Wealready 
knew that in the paddles the fleshy part was extended much behind 
the bony skeleton ; but the new specimen shows us that, in addition to 
the tail-fin, the Ichthyosaurs had a triangular fin on the middle of the 
back, behind which was a crest of horny excrescence compared to those 
of the crested newt. The tail fin is vertical and nearly symmetrical 
1 Ueber das Norian oder Ober-Laurentian von Canada. Stuttgart, 1893. 
