Earth's Surface during the Tertiary Period. 207 



\y covered our continents, and of which some still occur at the 

 present day between the tropics, had certainly ceased to exist in 

 our latitudes, since, according lo the researches of M. Adolphe 

 Brongniart, we find no remains of them in tertiary strata. At 

 the same period, the coral reefs which, during the silurian, and 

 probably also during the carboniferous epoch, extended in the 

 sea to Iglolik to the north of America, in latitude 69i°, and 

 which, during the Jurassic epoch, extended to Kirkdale in 

 Yorkshire, in latitude 544°, had also ceased to figure in our lati- 

 tudes, and since then have not reappeared. A lowering of the 

 temperature of the winters seems to M. Elie de Beaumont the 

 sole cause which can be assigned for this triple disappearance. 

 The temperature of the winter season in our latitudes must have 

 already been pretty low at the period of which we are speaking, 

 since the tree-ferns and the cycadeae could not continue to 

 exist on our continents, and since the species of polypi, which 

 have the power of grouping themselves in reefs, could not con- 

 tinue to live in our seas. On the other hand, the plastic clay 

 and the calcaire grassier of the environs of Paris, and even the 

 beds formed still more recently on the surface of France or the 

 neighbouring countries, present abundant remains of palms, of 

 crocodiles, and of large pachydermata. The temperature of 

 the winter season at the epoch of the calcaire grassier, must 

 then have been sufficiently elevated to allow these organic forms 

 to prosper ; and it might have been still a little further lower- 

 ed without causing them to disappear. By combining this 

 consideration with the preceding one, we obtain two limits, be- 

 tween which must be comprised the winter temperature of 

 the countries in which we live at the epoch of the deposition 

 of the calcaire grassier. These two limits approach each other 

 pretty closely, and the winters of Cairo fall precisely between 

 them. In fact, palms and crocodiles flourish in Egypt, and 

 hippopotami and other large animals live there. On the other 

 hand, tree-ferns and cycadeae do not exist ; and coral banks, 

 which border the coast of a great part of the Red Sea, stop at 

 the port of Tor in Arabia, about 2° of latitude south from Cairo. 

 As to the temperature of the hottest seasons of the year, it is at 

 present almost the same in all the countries which are not very 



