18 Tllli VICTORIAN NATUUALIST. 



everything, and eventually form strata of very great thickness. A 

 notable example of such a deposit is the Loess of China and 

 Central Asia, which is an accumulation of blown dust often as 

 much as i.ooo feet in thickness. In this way the ancient cities 

 of Nineveh and Babylon have probably been covered up. 

 Showers also might occasionally fall in these districts, often as 

 mud-rains, and this moisture would furnish the necessary con- 

 ditions of life for the land and marsh-loving shells which are often 

 met with in great abundance in these subaerial deposits. 



The phenomenon of mud showers frequently observed in 

 connection with volcanic eruptions is obviously related to that 

 of red rain, differing only in the source and nature of the dust. 

 The sediment in the former consists usually of crystalline par- 

 ticles and triturated volcanic material, whilst that of the latter 

 contains both mineral and organic particles. Upon both the 

 winnowing action of air currents may be observed, the finer and 

 lighter portion naturally being carried farthest from its source. 



The terrigenous deposits which occur off the west coast of 

 Africa, notably round Cape Verde, and contain much fine sandy 

 material, may in a large measure owe their origin to dust 

 storms, which carry a burden of fine material off the land, as 

 exemplified in the " sea dust " often collected from the decks of 

 vessels in that part of the Atlantic. 



The Red Bains of the Mediterraneaii Area and Their 

 Com.2')osition. — In the Mediterranean area showers of red rain are 

 very frequent, the south wind or sirocco bringing dust with it 

 from the Sahara Desert and meeting with the moist air of the 

 Mediterranean. In Sicily, around the harbour of Messina, a 

 curious illusionary effect is sometimes seen, which, accordmg 

 to some writers, appears to be directly connected with the 

 advancing dust-laden clouds. It is known as the Fata Morgana, 

 and supposed by the Sicilians to be the work of the fairy 

 Morgana. It presents the appearance of a screen extended over 

 the still, clear water, and reflections of edifices and other objects 

 are seen against it to a height of about 30 feet above the water's 

 level. (For sketches of this phenomenon, see Nature, 26th 

 February, 1903, p. 394.) 



The colour of the sediment from the red rain of the 

 Mediterranean coast regions and elsewhere is mainly due to the 

 ferruginous constituents of the soil which yields the dust, and it 

 varies greatly in degree according to its source. 



The composition of the sediment of red rain is often largely 

 silicious, due to the large proportion of quartz particles, and this 

 is frequently considerably increased by the presence of the 

 silicious frustules of diatoms which have been caught up from 

 freshwater lakes, or even from sub-fossil deposits which lay in the 

 path of the wind. This latter feature in the constitution of red 



