ig. meet Sak eS hee teal 
Geology and Natural History. 151 
th 
boniferous formations, with which the author is thoroughly fami- 
liar, and to which he mainly restricts his attention in this essay. 
lution 
instances generic types appear to merge into each other in such a 
way as to make it difficult to define their boundaries.” The 
longer he studies any group and the 
mens obtained from different localities, the more utterly does he 
distinguishing the 
This, surely, is what 
. Darwi 
(3.) J. W. Dawson: Annual Address of the President of the 
Natural History Society of Montreal, May, 187 4,—A considerable 
related matters. Substantially Principal L ’s views and 
aims are not very unlike those rof. Williamson, although the 
this may explain the contrast between their conclusions as to the 
abrupt introduction of types and forms, and those of Count 
gt : 
Williamson probably thinks that evolutionary hypotheses in some 
form are not unlikely to prevail ; Dr. Dawson, that they are already 
well nigh exploded. The former seems inclined to accept at least 
the probability of evolution for species and genera. . Dawson 
restricts its sway “to varietal and race forms,” which “ constitute 
make out, the difference between his “ varietal forms or conven- 
tional species,” which have arisen from “descent with modifica- 
