ORGANISMS IN TUFF 331 



contradictory- opinions were held. Some writers, from 

 the general stratified structure, correctly maintained the 

 marine origin of the tuff. Again, on the evidence of 

 enclosed land-plants and animals, some observers have 

 regarded it as a freshwater deposit, while others have 

 looked upon it as a terrestrial formation. It is true, 

 as I shall point out a little further on, that here and 

 there, especially in its upper parts, the tuff includes 

 intercalated bands of strata containing land and fresh- 

 water shells as well as bones of terrestrial mammals, 

 and indicating that the floor of the sea had been con- 

 verted into low land with brackish lagoons and lakes 

 of fresh water. But as regards the main mass of the 

 tuff of the Campagna, the question of its marine origin 

 may now be considered as definitely settled by the 

 researches of Professor Portis, of the University of 

 Rome. In specimens of different varieties of the 

 rock from all parts of the district, and previously 

 supposed to be entirely unfossiliferous, this careful 

 observer has found that foraminifera are often abun- 

 dant and well preserved. These organisms are un- 

 equivocally marine, swimming freely in the upper 

 waters and sinking when dead to mingle with the 

 silt or to form of themselves an ooze on the bottom. 

 We can thus understand how they might be borne 

 along above a sea-floor on which molluscan life was 

 hardly possible. 



If, then, cones of loose ashes and scoriae were thrown 

 up on the bottom of the sea, they would obviously 

 be apt to be rapidly lowered by the agitation of 

 currents and ground swell, while those which rose 

 above the surface of the water, as Lipari, Volcano 



