ON THE WAIANAMATTA SHALES. 83 
Origin of the Shales.—It does not seem very easy to account 
for the shales in the Hawkesbury sandstone. They are impure 
carbonaceous sandstones, with a good deal of silvery mica and such 
other minerals as would result from the decomposition of felspathic 
or granitic rocks with vegetable matter. It has been commonly 
agreed to call them lacustrine shales, but not a single item of 
evidence has ever been adduced that they occupied the sites of fresh 
or saltwater lakes. Fossil fish have been found but rarely, and 
stratified sandstone. We have, however, a horizontal finely 
inated stratification in many localities which looks like the 
action of water, and is not unlike some of the lacustrine strata 
of the central provinces of France. But every other clue dis- 
appears. No freshwater shells or remains have been found. The 
present lacustrine fauna of the world has few very immediate 
are well recognized freshwater fauna of the age of these beds. The 
freshwater bands of the Purbeck beds contains species of genera 
Which still exist, such as Paludina, Limnea, Planorbis, Physa, 
Valwata, Onio, and Cyclas. I do not think that we are justified 
vod grew in the place where they are now found. It seems 
have been a heathy stunted vegetation, such as grows even 
= all over the world. Probably Alethopteris was an Asple- 
Sy but hevertheless its habits were those of the living 
ere are places on the east coast of Australia where a level 
es. Soil gives rise in the course of time to a black carbonaceous 
t, such as we see here. It arises from the decomposition 
; ‘nts which grow on the surface. Someti 
ican « occur amidst them. Loose sand drifted ac hese 
doubt, to would entomb them, and cause them, I have little 
hale, “oe such appearances in section as the Hawkesbury 
that the; imagine that they represent long periods of time, an 
“ir highly fissile character is partly the effect of pressure. 
