GEOLOGICAL PALAEONTOLOGY 89 



faunas, some Confidence can be attached to deductions 

 with regard to climate, especially when shallow-water 

 forms are concerned. Thus the Lower Tertiary Molluscs 

 of England show a definitely subtropical facies, when 

 compared with living types ; those of the Oligocene 

 suggest temperate conditions, while those of the Pliocene 

 and Lower Pleistocene are distinctly arctic. In all 

 cases, however, terrestrial organisms (especially plants) 

 are more exposed to climatic influence than those in- 

 habiting the sea, and therefore give more delicate and 

 reliable indications of change. 



It is characteristic of partly enclosed gulfs to develop 

 "sour" qualities in tropical climates, owing to excessive 

 local evaporation. Concentration of the sea-water (such 

 as that commonly found in coral-lagoons) adversely 

 affects the fauna, giving stunted races, prone to disease. 

 Perhaps the small size of most fossils in the Magnesian 

 Limestone (and in many Triassic dolomites on the 

 Continent) may be ascribed to such circumstances, and 

 so give indirect evidence of the climatic conditions 

 prevalent in the two periods. 



