6 OBSERVATIONS ON CANADIAN BIRDS. 
occurring not only in the Trimetric and in the Monometric Systems, new 
examples of which (as regards the latter) are described above ; but also in 
the Monoclinic System, in which until now, none have been announced ; 
and in which, moreover, by some observers, these crystals have been 
thought of impossible occurrence. 
(2.) Although thus shown to occur in various systems, none have 
yet been recognised, with certainty, amongst minerals or in artificial 
crystals of the Hexagonal System. 
(3.) Hence—from the facts given in onitlastiond 1 and 2—the 
assumed Hexagonal crystallization of snow, if not disproved, becomes 
at least of very doubtful acceptation. 
NOTICES OF BIRDS OBSERVED NEAR HAMILTON, C. W. 
BY THOMAS MC ILWRAITH ESQ. 
To those who are aware of the many additfons which have of late 
years been made to the list of American birds, as well as of the difference 
of opinion which still prevails among authors regarding the identity 
of certain species, it must be evident that our knowledge of this 
branch of our Natural History is by no means complete. Probably, 
the greatest difficulty in the way of getting anything like conclusive 
information on the points in dispute ,arises from the migratory character 
of nearly all the birds of North America, and the remote regions in 
which they spend the interesting period of reproduction; so few in- 
deed, can be called resident, that if we take any point on the continent 
and ascertain the number of species which residethere all the year round, 
we are astonished at the smallness of the list; in our own case it would 
not exceed a dozen species, and even of these, it is doubtful whether 
those we see in summer are not replaced by other individuals of the same 
species, coming from the north at the approach of winter. 
Another perplexing subject to the ornithologist has ever been, the 
changes of plumage which birds undergo at certain periods of their 
lives, or at particular seasons of the year. This is most remarkable 
among our rapacious birds, many of which do not come to maturity 
in plumage till their 4th or 5th year, and having been found breeding 
in the immature dress, have frequently been described as distinct 
species. 
