March, 1907.] THE VICTORIAN NATURALIST. 215 



Though bluestone is so tough, yet it will decay under 

 the action of rain water. The felspars decompose, the 

 soluble parts wash away, the iron dissolves out, and at 

 last we get a white clay. These changes were clearly 

 traceable step by step in the cliff'. If auring decompo- 

 sition plant-roots penetrate and decay, then the mixture 

 of decaying rock and plant produces the rich chocolate 

 or black soil characteristic of onr bluestone plains, and 

 so eagerly sought after by the agriculturist. 



Then we turned our attention to the high cliffs of sand, 

 cemented by iron-rust, which are so marked a feature of 

 parts of the Moxnington coast. The top of the cliff's is 

 crowned by a dense growth of coast tea-tree, sheoak, and 

 honeysuckle. For the first 20 or ,■^0 feet downward the 

 sands are white ; then gradually they become more and 

 more mixed with iron-rust. The colour changes from 

 yellow to a rich dark-brown, or even in places to a brown- 

 ish-red. Lower still, the colour fades somewhat, and a 

 uniform brown reaches to the bottom of the cliff. By the 

 colour we can, even at a distance, judge the proportion of 

 iron rust in the sands. The uppermost part contains 

 almost none, except for a band a couple of feet from the 

 top. This is the iToo-pan, and we discussed it subse- 

 quently. The lowest part at the foot of the cliffs con- 

 tains less iron than the middle series below the white 

 sand. 



The stratification lines, which mark the successive sheets 

 of sediment, are horizontal, but the white band follows 

 the surface of the ground. It has been formed subse- 

 quently to the piling of the sediment. All the sands were 

 once brown. Something has removed the iron from the 

 upper layers, and added it to that already in the middle 

 layers, while the lower layers are unchanged. 



Bacteria are popularly regarded as entirely noxious and 

 injurious. But many of them promote decay of organic 

 material. Without the decay, all plant and animal food 

 would be soon locked up. As the scrub we see on the 

 cliff-top dies, bacteria attack it. In the complicated series 

 of changes they bring abont, abundant acids are formed, 

 which are capable of dissolving iron as well as other 

 things. They remove all the iron from the surface layers. 

 and, as they alter their composition deeper down, the iron 

 is again set free, to increase the amount in the middle 

 layers. 



In the afternoon, the structure, composition, and pro- 

 ducts of decay of the Mount Martha granite were ex- 

 amined, and the characteristic flora, of granite under 

 similar conditions of climate was pointed out. 



