326 T. G. TAYLOR AND D; MAWSON. 
2 and 3. These tuffs were much decomposed and of no 
special interest. | 
2.—e. Basic Dykes.—T wo large basic dykes occur in 
cuttings on the Mittagong Coal Co’s line near Kell’s Creek. 
They are highly decomposed, but are undoubtedly formed 
of dolerite in the centre, with a zone along the sides of a 
fine grained rock. The latter presents the same charac- 
teristics as that constituting the more common dykes of 
the district termed by J. B. Jaquet, syenite. That the 
more acid rock should separate out first in a rock magma 
is quite contrary to the commonly accepted law. Hence 
it seems possible that many of the decomposed dykes of the 
district are basic and not intermediate. This view is also 
strengthened by the fact that in other parts of the district 
where sections of the dolerite can be obtained (as at 
Mittagong Coal Co’s adit) the dolerite is always fringed by 
a narrow belt of basalt. The above dykes are similar in 
structure and of sufficient interest to warrant a description 
of one of them. The second one occurs in a cutting about 
one-third of a mile past Kell’s Creek. The sides are 
bounded by quartzites exhibiting slickensides and inter- 
penetrated by smaller dykes. Bands of limonite and chalce- 
dony occur near the edges. Its direction is 10° Hast of 
North, and width about two chains. It is undefined to 
the south but extends some distance to the north. The 
dolerite has weathered into spheres with concentric crusts. 
2.—f. Picrites.—In the channel of Jellore Creek, about 
half a mile above its junction with Powell’s Creek occurs 
the following series of dolerites and picrites. About one- 
third of a mile below the clearing (on the path from Chant’s 
Farm to Mount Jellore) the creek cuts through a dyke of 
coarse-grained dolerite weathering spberoidally but con- 
taining undecomposed pieces in the interior. This is 30 
yards wide and carriesa little pyrites. Then come 15 yards 
