xlvi PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



A great part of the plain of Pampliylia is composed of modern 

 travertine, beds of which are forming at the present time, from the 

 prevalence of springs loaded with carbonate of lime held in solution by- 

 carbonic acid, as is common in countries bordering on volcanic re- 

 gions. This travertine, where it reaches the coast, forms cliffs from 

 20 to 80 feet high, and at various distances inland there is a repetition 

 of heights resembling the line of cliffs. Along the shores of Lycia 

 there is an extensive formation, now in progress, of a conglomerate 

 composed of water-worn pebbles, interstratified with beds of mud and 

 sand, cemented into a hard rock by calcareous infiltrations, but yet 

 so preserving the external appearance of a shingly beach, that boats 

 are in danger of striking against a rock, where those unacquainted 

 with the coast are expecting to run them up on a loose yielding bed. 



By the blocking up of the mouths of some of the rivers, by shift- 

 ing sands, lagoons and marshes are formed ; the water is at first salt, 

 but if the barrier endures long enough, it becomes fresh, and is 

 peopled with freshwater mollusca. Thus at Maori, where such 

 changes have taken place within the historical period, as already 

 stated, lagoons of this kind are filled with myriads of the Cerithium 

 mammillatum, a moUusk capable of enduring great changes in the 

 quality of its native element. These alternations of salt, brackish 

 and fresh water, must produce deposits with corresponding changes 

 of character, so that, as Mr. Forbes observes, a section of the plain 

 would doubtless show many alternations of such strata ; and he adds 

 this important remark : — ''The history of life upon our globe, the 

 in-coming of new species and the perishing of old ones, is only the 

 history of elevations, depressions, and temporary conditions, varied 

 by an occasional convulsion, differing only in degree from those which 

 have determined the zoo-geological features of the coast of Lycia." 



A case analogous to such modern formations is described by Mr. 

 Forbes as occurring in the older pliocene freshwater beds in the 

 island of Cos, and which exhibits a phsenomenon of great importance 

 in palaeontology, one particularly instructive to those who have a ten- 

 dency to multiply species on insufficient grounds : — " The freshwater 

 beds in Cos contain mollusca of the genera Paludina, Melanopsis, and 

 Neritina, distributed in three distinct horizons, throughout the 

 vertical thickness of the stratum, each horizon in the series being 

 characterized by a peculiar form of Paludina and of Neritina, not 

 present in the other two ; and in the two lower horizons there are 

 two species of Melanopsis peculiar to each. They have the appear- 

 ance of very distinct well-marked species, but on careful examination 

 it is evident that they are of the same species, presenting varieties 

 caused by the animals having lived in alternations of fresh and salt 

 water." He then enters into a minute explanation of the operation of 

 these changes of condition, and thus concludes : — " Such an explana- 

 tion is consistent with what we now know of the modes of variation 

 among freshwater mollusca, which, at first glance, appeared to afford 

 strong support to the notion of a transmutation of species in time." 



When certain peculiar marks on the surface of slabs of new-red-sand- 



