68 SYNCHRONISM OF THE PHENOMENA 



current. At other times, the currents being slight 

 were only sufficient to wash down the finer sediments 

 and the small fragile land shells without destroying 

 them. In the few rare cases where marine or flu via tile 

 shells occur, they have been derived from some sub- 

 merged shore or river. All the organic remains 

 proper belong to the same geological period that is 

 to say, to the late Quaternary or Pleistocene, though 

 they show that variation in the distribution of species 

 which marks, as at present, the influence of climate, 

 soil, and altitude. 



Not only have the several forms of the Rubble-drift 

 an origin due to a common cause, but the unity of the 

 whole of the phenomena is further evinced by the 

 synchronism of the rents in the rocks with the 

 ossiferous breccia lodged in them. Had these fissures 

 been open at a period anterior to the Eubble-drift 

 the lower stratum of animal remains must have 

 belonged to an older fauna, and the breccia would 

 have been of a less homogeneous character. There 

 would have been successive layers in accordance with 

 differences of age and conditions. There is however no 

 evidence to show that the fissures were open at any 

 previous period, but on the contrary, much to show 

 that their formation was the result of the one set of 

 land movements. At the present day, it is common 

 for fissures in the ground to open during earthquake 

 movements, but they generally soon close again. In 

 this case we have reason to suppose that the fissures 

 were so speedily filled during re-elevation of the land, 

 that they were prevented from closing, and thus re- 



