34 
SMITH’S MILL, OCTOBER i6th, 190a. 
On the 16th October the Society made an excursion to 
Smith’s Mill, when the Botanical, Entomological and Geological 
sections of the Society were all represented. In the unavoidable 
absence of Mr. A. Gibb Maitland, F.G.S., the leadership devolved 
upon myself. 
On arrival at Smith’s Mill the party necessarily divided, 
the entomologists proceeding to the South-east, the rest of the 
party to the South-west. In preparing the following notes, I am 
indebted to our President for the botanical information and 
to Mr. H. M. Giles, F E.S., for the entomological. 
Geological - — In the gravel pits and brick pits immediately 
to the South-west of the station the structure of the widespread 
laterite capping and its relationship to the underlying white 
clay and granite is rendered obvious. The laterite consists 
usually of bauxite and liinonite in about equal proportions, in 
one place at Smith’s Mill it was seen to contain so little iron 
as to become a sufficiently pure bauxiie to be used for the com- 
mercial production of aluminium. At a short distance on either 
side it passes gradually into a much more highly ferruginous 
material. 
The origin of this laterite is a problem of great interest which 
is only now being solved. So far as this part of Western Aus- 
tralia is concerned its origin appears to be as follows: — In the 
wet winter season lain water charged with carbonic acid pene- 
trate c to a considerable depth into the giande, which it attacks, 
converting it slowly into a mixtuie of quaitz and kaolin and 
dissolving all alkalis, magnesia, lime, iron and pait of the alumina. 
In the diy summer easons as the water in the ruiface soil rva- 
poiates, the mineralised watei from below rises to the surface 
and evaporating there deposits all its mineral matter. Of this 
latter the hydrates of iron, aluminium and titanium remain 
permanently as a laterire cap, whiLt the magnesia, lime and 
alkalis are cairied away by smface vateis. 
Proceeding westwaid along the lailway, gianite and oc- 
casionally dioiite oi diabase dykes are seen in the cutting' . The 
granite contains much microline and in two places includes a 
narrow pegmatite vein in which microline is very plentiful. 
About half way between Smith’s Mill and Darlington the 
surface effects of a fault are to be seen. This fault passes under 
the railway line at a small angle and brings to the surface at 
this point a large quantity of water charged with silt, the result 
being a very insecure foundation for the line which has in 
consequence, constantly to be repaired. 
The party proceeded to Darlington, but time did not permit 
of the examination of the interesting belt of mica schist oc--. 
curring in the granite there. 
