Occasional Notes. 177 
of the country in the neighbourhood of gold deposits, 
and the latter the rocks dire6tly in conta6l with the 
auriferous veins. Among the silver ores, many of which 
are also rich in gold, is a specimen of silver sandstone 
from Utah — an ore which when first discovered was 
pronounced to be a fraud by experts, who evidently 
regarded it as common sandstone soaked in a silver 
solution, but from which, however, it appears that millions 
of dollars have since been paid as dividends. In 
addition to the ordinary metallic ores, are to be seen 
various minerals of economic importance, such as speci- 
mens of gypsum and phosphorite, used as fertilisers and 
for other purposes ; of asphaltum and bituminous sand, 
used for roadways, sidewalks and roofings, etc., and of 
Wollogongite or Australian coal, used (mixed with ordi- 
nary coal) in the gas works to enrich the ordinary gas. 
Interesting specimens are also shewn of diamond- 
iferous sand, and of Itacolumnite, the associate rock of 
diamonds; of graphite, which in California, however, is 
not of the first quality ; of arragonite, so largely used for 
ornamental work, and of dendrites on country rock, which 
on this, as on other rocks such as granite, slate, etc., of 
which specimens are shewn from British Guiana and 
from Wales, are due to the presence of manganese 
under the form of sea-weed-like tufts. 
Change of plumage in Birds. — Among the most 
interesting features of bird-life must be ranked the very 
marked changes of plumage undergone by some, perhaps 
the most strikingly coloured birds, while passing from 
their immature to their adult condition : and though the 
z 
