4 1 2 Tertiary Formations : fake n 



Tierra del Fuego, to find these two great conchological 

 provinces united into one." Hence it is remarkable that 

 four or five of the fossil shells from Navidad, namely, 

 Voluta alta, Turritella Patagonica, Trochus collaris, 

 Venus me r ridionalis, perhaps Niitica solida, and per- 

 haps the large oyster from Coquimbo, are considered by 

 Mr. Sowerby as identical with species from Santa Cruz 

 and Port Desire. M. d'Orbigny, however, admits the 

 perfect identity only of the Trochus. 



On the Temperature of the Tertiary Period. — As 

 the number of the fossil species and genera from the 

 western and eastern coasts is considerable, it will be 

 interesting to consider the probable nature of the 

 climate under which they lived. We will first take the 

 case of Navidad, in lat. 34°, where thirty-one species 

 were collected, and which, as we shall presently see, 

 must have inhabited shallow water, and therefore will 

 necessarily well exhibit the effects of temperature. 

 Referring to the Table given in the previous page, we 

 find that the existing species of the genera Cassis, 

 Pyrula, Pleurotoma, Terebra, and Sigaretus, which are 

 generally (though by no means invariably) characteristic 

 of warmer latitudes, do not at the present day range 

 nearly so far south on this line of coast as the fossil 

 species formerly did. Including Coquimbo, we have 

 Perna in the same predicament. The first impression 

 from this fact is, that the climate must formerly have 

 been warmer than it now is ; but we must be very 

 cautious in admitting this, for Cardium, Bulla, and 

 Fusus (and, if we include Coquimbo, Anomia and 

 Artemis) likewise formerly ranged farther south than 

 they now do ; and as these genera are far from being 

 characteristic of hot climates, their former greater 

 southern range may well have been owing to causes 

 quite distinct from climate : Yoluta, again, though 



