12 Classification of Rocks in New Countries. 
As regards the age of the igneous rocks of Tas¬ 
mania I can only say a few words. That of the 
granite I do not know. Some of the greenstones, at all 
events, if not the greater portion, are among the oldest 
rocks in the south-east corner of the Island. The sand¬ 
stones, unaltered and undisturbed, abut horizontally 
against them, and the conglomerates contain fragments 
of greenstone as rounded pebbles. The basalts and traps 
appear to be much more modern ; they cut through and 
alter the sandstones, and sometimes, as at Salt Water 
Creek in Norfolk Bay, and, as mentioned by Mr. Darwin, 
near Hobart Town, they have flowed in part as subaerial 
lava, forming now pumice and scoriae. The trap which 
has tilted the recent limestone mentioned above must bo 
still more modern than it. 
I may, perhaps, be pardoned if I mention in conclu¬ 
sion, as an observation springing directly from the 
subject, the want there appears to be of a geological 
survey of these colonies. They appear to contain much 
mineral wealth, with which speculation is already busying 
itself: thousands of pounds w T ill probably be thrown 
away by misdirected efforts, which a mere outline survey 
of the districts, conducted on sound principles, would 
direct into proper channels. If it were merely to point 
out those spots in which all mining attempts would be 
plainly fruitless, much good might be done—much time 
money, and labour probably saved; but positive and 
direct benefits could hardly fail to result from a good 
survey, not only to the mining interests, but also to the 
agricultural, the engineering, and all other operations 
connected with the soil or with the rocks below it. 
