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the like). When such discharges do take place, they are usually occasioned hy the 
diminution of the internal heat. Hence it would appear that ashy deposits from basaltic 
volcanoes are among the last stages in their history. 
“ In the Cooktown and the Ilerberton districts there do occur beds of ashes 
which emanate from basaltic cones ; but whether these are of later date than the 
Burdekin-Einasleigh lavas, yet awaits proof. 
“ Throughout the area occupied by the lavas, there is a very great difference both 
in texture and colour. Some portions are very vesicular and slaggy, whilst others have 
that peculiar ‘ ropy’ or wrinkled appearance, characteristic of lava streams, which have 
flowed slowly from their source ; others, again, are fairly compact. In colour they 
vary from bluish-grey to bright red, with all degrees of variation. In cavities in the 
basalts beautiful specimens of chalcedony can sometimes be seen. 
“ The black soil formed by the decay of the rocks is often crowded with fragments 
of semi-opal. 
“ A number of slices of the basalts have been prepared and submitted to 
microscopic examination. 
“ A partial analysis of a specimen from the Valley of Lagoons has been made for 
me by Messrs. Coane and Clarke, Charters Towers, with the following result : — 
Combined silica ... ... ... ... ... ... ••• 43 ’8 per cent. 
Tree silica,.. ... ... ... ... ... ... ••• „ 
Iron ... ... ... ... ... ... ... ... 13o „ 
“ One example — viz., that from Mount Eazorback — would be more correctly 
described as a magma-basalt, from the fact that the minerals are scattered through a 
glassy matrix or magma, which by ordinary^ transmitted light is of a brownish colour. 
This, however, is merely a local occurrence ; a few yards distant from the summit of 
Mount Eazorback the basalt resumes its ordinary type. 
“ The felspars, which make up the larger piortion, occur as long lath-shaped 
crystals, showing plagioclastic twinning. They are remarkably clear and fresh, and 
contain numerous minute inclusions. 
“ Olivine, in crystals and crystalline grains, is altered along its edges into a 
ferruginous product. Sometimes the whole of the crystals and grains have undergone 
this alteration, but generally the decomposition is found to extend only a short distance 
from the periphery. 
“ The augite occurs in long brownish crystals, often showing faint dictoroism, 
and magnetite in grains. 
“ In the slices of any of the basalts which were examined, there occurred a little 
clear transparent isotropic matter. 
“ Some portions of the glassy matter contain minute particles of some doubly 
refracting mineral (quartz ?). 
“ The partial analysis made by Messrs. Coane and Clarke shows the presence of . 
a small quantity of free silica, and to this the isotropic matter may be referred. 
“ There existed no primary quartz in any of the slices of these basalts. 
“ All over the plateau numerous small ‘ puys,’ the remains of orifices from 
which these basaltic lavas emanate, are met with. 
“ Ascending the Valley of Eeedy Brook to its head, and crossing the divide into 
the waters of Gunnawarra Creek, a tributary of the Herbert Eiver, a good idea of 
the mode of occurrence of the lavas and the structure of the volcanic foci can be 
obtained. 
“ Much more work will be necessary before a full description of the whole of the 
sources of the lava on the plateau can be obtained. 
