THE GEOLOGY OF MITTAGONG. 349 
feet between the top of the upper marine and the bottom 
of the Newcastle Bulli coal measures; this outburst was 
followed in regular sequence by basaltic flows above the 
coal measures. 
Much more data is at hand to prove that volcanic activity 
was contemporaneous with sedimentation over this sub- 
sidence area, aS for example the Kiama volcanic series, 
the chocolate and purple shales of the Narrabeen series etc. 
Further evidence which has perhaps hitherto been over- 
looked is the occurrence of foreign pebbles of igneous rocks 
in the old denuded volcanic pipes of which that at Pennant 
Hills and at ‘‘the basin’’ on the Nepean are examples. 
Differentiation in the lower portions of the neck and subse- 
quent tearing off and floating up of the fragments cannot 
be ascribed as the origin of all these varieties’ of included 
fragments. A good example is that of a large fragment, 
over one inch in length of orthoclase found in the basalt 
over the Bowral railway tunnel.’ It would appear then, 
that the sediments in this area of subsidence form an 
immense thickness of rock, which like a mighty tomb has 
buried within it, tier upon tier, the ruins of once active 
volcanoes, but whose only memory now is an occasional 
thin bed of lava or a belt of purple shales hardly recognis- 
able as being of volcanic origin. 
In conclusion we desire to thank Mr. EK. C. Larkin of 
Fitzroy lron Works for his hospitality during our numerous 
visits, and Mr. G. Saunders for aid in field work on the last 
visit, and to express our gratitude to Professor David and 
Mr. H. Jevons psc, for help on every occasion where help 
was necessary. 
* Some of these are more acid than the enclosing lava. 
? Vide antea page (325). 
