THE GEOLOGY OF MITTAGONG. 513 
and as the coal seams are porous it is evident that a fair 
amount of soakage must take place into the coal seams 
from either side of the valley, which would later on rise 
up to the surface through any available cracks such as 
dyke and fault fissures, etc. Moreover as the coal seam 
is intruded by the eruptive rock in the anthracite valley, 
and as at least 20 feet of it next the seam is decomposed 
into a white trap, it is only natural to suppose that all the 
iron from it has been dissolved out by the water circulating 
along the seam, this iron augmenting the supply if not 
furnishing almost the whole of that rising to the surface 
in the waters of chalybeate springs. Summary of argu- 
ments in favour of its origin from the eruptive rocks :— 
1. In most of the decomposed dykes of the district a 
narrow parting of limonite occurs between the dyke 
rock and the sedimentary rock. 
2. That these springs are always found in the vicinity of 
eruptive rock. 
3. What has become of the iron leached out of the trap 
in the anthracite valley ? It could not have run directly 
into the Nattai, as the dip of the strata is inwards. 
4, The iron ore contains all and only the constituents of 
the eruptive rock, even to Titanium, which is usually 
uncommon in sedimentary formations. 
od. It could not be derived from the sedimentary forma- 
tions for reasons already given under that head. 
2. Tertiary Deposits. 
The drifts and gravels occur almost invariably wherever 
the basalt caps have protected them from denudation. They 
consist of rounded fragments of quartz and basalt cemented 
together by ferruginous material so as to form a con- 
glomerate, which usually occurs as rounded blocks around 
the edges of the overlying basalt. The contained basal: 
U—Oct. 7, 1903. 
