77 
exotics, but the nucleus of a valuable ancillary to the 
Botanic Gardens. 
An arboretum such as that at Sherwood cannot, of 
course, aim at more than a representative collection of 
Australian trees, and is not intended for other types of 
plants. To that extent, it is limited in its objects. There 
are Council reserves of native vegetation in the immed- 
iate vicinity of the city, notably at Mount Coot-tba, but 
they have no educational pretensions . The great 
National Parks movement, which began with the declar- 
ation of the Witch’s Falls National Park of 324 acres 
on Tamborine Mountain has opened up a new develop- 
ment. Areas of natural vegetation have been reserved 
for all time in chosen localities throughout the length 
of Queensland, both on islands and the mainland. Some 
>f them are small, like Witch’s Falls National Park, 
hut some are thousands of acres in extent. It may be 
argued that these are not botanic gardens; they are 
reserves of native vegetation. In some of them, though, 
graded paths and labelled trees give the visitor the 
opportunity of seeing what is possible in few botanic 
gardens — plants growing in their natural habitat, in 
youth, maturity and old age, with all their associated 
species, animal and vegetable. Such national parks are 
natural botanic gardens of a type that can be never 
duplicated anywhere else. They are complementary to 
the botanic gardens of the cities. 
NOTES ON ROCKS, No. 2 
SEDIMENTARY ROCKS 
By JACK T. WOODS 
Sedimentary rocks are derived from other rocks hv 
processes which operate at or near the surface of the 
earth’s crust. These processes are always going on and 
many may be easily observed. Sedimentation includes 
the breaking up of the parent rock mass (weathering) . 
the transportation and deposition of the products and 
their consolidation into rock. This sequence can cease 
temporarily at any point and parts of it may be repeated 
before the final product — the rock — is formed. 
Weathering. 
Weathering lias two inter-related aspects, physical 
disintegration and chemical decomposition. Several 
