198 
Geology of Sydney. 
where we find it ? Geologists assure us that for the 
most part the coal plants flourished on old land 
surfaces now represented by the under-clays. The 
growing plants, acted on by the sun’s energy, separated 
carbon from the atmosphere, just as living plants do. 
There is, therefore, much truth in the old measure — 
41 ’Tis the sun’s old heat that cooks our meat, 
3 Tia his bottled-up beam that gives our steam . ,J 
When we ask if the plants that formed coal grew just 
where the coal is formed, we are opening up a question 
that was at one time much debated. The “ drift 
theory supposed that the vegetable matter which 
forms coal grew in forests, and was drifted into lakes, 
or even into the sea, and in time settled to the bottom 
Facts are, however, against this theory. Under every 
bed of coal we find an “ under-clay.” These “ under- 
clays represent the old soil on which the vegetation 
flourished. 'Trees have been found standing erect in 
coal-seams, with the roots striking into the “ under- 
clays.” The absence of sand and mud shows that the 
vegetable matter was not drifted. Besides, it is not quite 
intelligible how pure seams of coal of great extent 
could have been formed by drifted materials. The 
transition from a peat-bed to a coal-seam is a change 
in keeping with observed facts. It has been noted, 
too, that the “ under-clays” are deficient in alkalies, 
these having evidently been extracted by the 
growing plants. The ashes left, on burning the coal, 
give up these alkalies once again. When the vege- 
tation that made our coal was growing, the coast-line 
