420 Notices of Meinoirs — Prof. J. W. Gregory — Deserts. 



been suggested that the existing deserts are now increasing, but the 

 evidence (recently summarized in the Geographical Journal, vol. xliii, 

 pp. 148-72, 293-318, 1914) indicates that there has been no general 

 expansion of the desert areas, which are, however, in some places 

 shifting their positions in consequence of local climatic changes. 



Deserts are not absolutely incurable, and, owing to a better 

 knowledge of how to use their slight and irregular rainfall, many 

 once-desert areas are now in profitable occupation. When suitably 

 watered, deserts may be extremely prolific ; for their soils are often 

 rich in immediately available plant-foods which have accumulated 

 during the long period of rest. The desert soils are often very deep 

 and their crops are nourished from an unusually thick layer. The 

 desert soils especially accumulate salts of potash and lime, which 

 would be leached out of them with a heavier rainfall. 



Australian soils have as a rule less than the usually accepted 

 minimum of phosphoric acid required for cultivability. Thus, 

 according to the analyses collected by Professor Cherry, English soils 

 have "098 per cent of phosphoric acid, American ordinary soils '116, 

 and American clay soils •207 ; yet the heavier soils of Victoria have 

 only -06 and the light soils of the mallee only '047. 



Professor Cherry's results are confirmed by a varied series of 267 

 soil analyses from Germany, Holland, Spain, Hungary, Jersey, 

 Sweden, Russia, Java, Sumatra, India, Sandwich Isles, the Congo, 

 the Cameroons, Senegambia, German East Africa, South Africa, and 

 Madagascar. The number includes 22 British and 57 from various 

 outlying parts of the United States of America. In these 267 

 analyses the average of phosphoric acid is -157 per cent. 



Most soils contain more phosphoric acid in the soil than in the 

 subsoil — an advantage which Australian soils do not share. A series 

 of 220 analyses, collected for me by my assistant, Mr. P. Brough, 

 which show the composition of various soils and their subsoils, give 

 an average of "158 of phosphoric acid in the soil and 'ISo in the 

 subsoil ; and, excluding a couple of subsoils in which the result is so 

 high that there must be an inclusion of some phosphatic fragment, 

 the ratio of phos[)horic acid in soil to subsoil is 16 to 13. In some 

 cases the soil may owe its excess of phosphoric acid to mannre ; but 

 the excess is often shown in cases in which the land has not been 

 manured. 



This series of analyses confirms the generally accepted fact that 

 Australian soils are exceptionally low in phosphate and that outside 

 Australia the soil is usually more phosphatic than the subsoil. 



The only explanation of these two abnormal features of Australian 

 soils that appears at all satisfactory is that proposed by Professor 

 Cherrj'- ; according to his interpretation the phosphatic accumulation 

 in the soil is due to the action of mammals, and owing to the poverty 

 of Australia in mammalian life no such phosphatic enrichment of the 

 soil has taken place. Soils, therefore, in Australia, which appear to 

 be incurably barren, may, owing to their other excellent qualities, 

 prove of high value if their poverty in phosphoric acid be remedied 

 by manure. 



J 



