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typical examples of these survivals. Among the coal-beds of still older age in South Africa, India, Tonquin, Australia, and New Zealand the fossil plants which are identical (but of genera now extinct) are still more numerous.

It is thus seen that the autochthonous flora of Australia must have been long isolated from the rest of the world. Even the immigrant forms which mixed the flora of the eastern coast were cut off from reinforcements, and in many cases have died out altogether. The purity of the autochthonous flora still occupying the south-west corner of Western Australia is proof that the immigrant flora invaded eastern Australia while yet the western half of the continent was a detached island. It is further proof that since the period of the fusion of this western island with the land mass in the east there has existed an arid or "Eremian" region dividing the continent into a north coast section and a south coast section, except for the narrow eastern belt formed by the Blue Mountain cordillera in New South Wales. Across this Eremian central region a large section of the immigrant flora could not spread; while competition with the local forms in the east, reinforced continually by autochthonous forms from the west after the continent had become one compact land-mass, caused many of the immigrant families to die out altogether and others to become much modified in structure and in numbers.

What caused this great development of tree-life throughout the world at the beginning of the Tertiary period, and its shrinkage into highly-specialized forms with restricted habitats later in the Tertiary period (and continuing down to modern times), is a riddle yet unsolved. It has been suggested that the development of monocotyledons, especially the grasses, which took place after the Miocene period and is still proceeding, though not yet at culminating point, affords a sufficient explanation of the modifications of both flora and fauna. Certain it is that the teeth of the early land mammals were better designed for twig-breaking, fruit-crunching, gnawing, and root-grubbing than they were for browsing on pastures. It is the mammals of today which are specially adapted to browse on prairies, in meadows, or in glades. But for their offices in keeping down grass growth and insect life the most productive regions of natural growth would be under the continual menace of destruction by fire, and the fauna become the victims of a holocaust when fires took place. It is due to the outpouring of lava streams and their complete covering of drift deposits over wide areas that most of the fossil plants in eastern Australia have been preserved to us. Tin ore and gold being also in the detrital matter thus preserved the fossils have been brought to light by the work of the miner's pick. So little exploration has been done as yet in the western half of the continent that it is impossible to surmise the extent to which our present knowledge may be supplemented from that source when it shall be explored. The broad generalizations already established do not, however, seem likely to be very much amended.

The character and aspect of the Australian flora has been often described, and it is needless to repeat the descriptions here. It was Robert Brown who first drew attention to the shadeless character of the trees owing to the leaves being set edgewise on the stems, and that both sides of the leaves were alike in consequence. It is a popular belief that all of the Australian trees are evergreen, that the trees shed their bark instead of their leaves. But there are a few which are deciduous, though they are not all markedly so. In the Cape York Peninsula the following deciduous trees occur, and some of them also occur in tropical Western Australia:—Cochlespermum Gillivræ, Bombax, Malabarica (the silky cotton-tree), Sterculia quadrifolia, Melia compositæ (white cedar), Cedrela toona (red cedar), Sesbania grandiflora, Erythrina Indica, Castanospermum Australe (Moreton Bay chestnut or "bean tree"), Albizzia procera, Sarcocephalus cordata (Leichhardt-tree), Eucalyptus platyphylla (poplar gum- tree), and Ficus colossa.

There are now some 200 naturalized plants in Queensland which have made good a new home for themselves in that tropical corner of Australia; while South Australia, in the temperate region of the south, has no fewer than 348.

The rainfall map exhibits very clearly the three natural divisions of the floral regions of Western Australia. There is the tropical north separated from the temperate south-west by the dry Eremian region, which extends from the west coast right across Central Australia to the western foot of the eastern coast range. This dry region, with its great extent, is due to the prevalence of south-east winds—really the south-east trade wind—which normally blows right across Australia from the Great Bight to the north-western coast. These winds in their course go from a cool to a warmer latitude, and as there are no high mountains to chill them they not only retain the moisture they bring from the south coast, but add to it by evaporation of any water met with along their journey inland. The north-west coast is therefore a region watered by rainfall only when the cyclonic depressions in their passage down the Indian Ocean on its Australian side (a passage which they continue along the south coast after rounding Cape Leeuwin) get drawn in to strike the coast above the North-West Cape, and so take a "short cut" across to