PHYSICAL GEOLOGY. 183 



Thomson, Prof. W. The * Challenger ' Expedition. Nature, vol. xi. 

 pp. 95 and 116. 



Sand dredged in Agulhas current at 98-150 fathoms consisted of 

 casts of Foraminifera in a silicate of alumina, potash, and iron, allied 

 to Glauconite. A table of the nature of the bottom at 160 stations in 

 the Atlantic and Southern Oceans shows that three different deposits 

 were met with : — -Ist. Ordinary Glohigerina-oozQ, down to a mean max- 

 imum depth of 2250 fathoms. 2nd. Grey ooze, at a mean depth of 2400 

 fathoms. 3rd. Red clay, at 2700 fathoms and upwards. The author 

 believes that as the Glohigerina-BheVLs sink slowly down from the sur- 

 face, the carbonate of lime is dissolved out by carbonic acid, which is 

 found in excess at great depths, and that the red clay is the insoluble 

 residue. The grey ooze forms a transition from the Glohigeriiut-oozQ 

 to the rod clay. A. H. G, 



Ward, Thomas. The great European Salt Deposits, with a Theory 



as to their Origin. Proc. Lit. <fe Phil. Soc. Liverpool, no. xxviii. 



pp. 163-187. 



The chief salt-districts are noticed under 10 heads. The theory is 



that the salt-deposits " owe their origin entirely to the elevation 



of the mountain-chains with which they are so intimately connected," 



during which " small valleys and ravines would be cut off from 



connection with the sea by ridges of land, and would form salt lakes 



and lagoons." "W. W. 



Williamson, Prof. W. C. Deep-Sea Researches. Nature, vol. xi. 

 p. 148. 



States that the explanation given by Prof. W. Thomson of the 

 origin of the Red Clay (see above) had been already suggested by 

 himself. A. H. G. 



Wilson, A. S. On some chemical aspects of Physical Geography. 

 Chem. News, vol. xxx. no. 763, p. 14 ; no. 764, p. 26. 



Clay and finely divided earthy matter have the power of absorbing 

 various salts from solutions. The author thinks that compounds of 

 ammonia may be thus removed from rain-water as it percolates through 

 the soil, which .thus becomes enriched while the water is purified. 

 Fine river-sediment brings down with it salts of potash, ammonia, and 

 phosphoric acid, derived from sewage and other impurities, whence the 

 fertility of deltas and alluvial soils. The author also believes that the 

 " red mud" dredged by the * Challenger' is an incipient slate rock, 

 and publishes three analyses of British slates. A. H. G. 



