CIMOLIOSATJRUS RICHARDSONI. 173 



it is now receiving in addition to what it has in virtue of the 

 temperature of space. The temperature would be lowered 

 to a condition of climate as severe as that of North Green- 

 land at the present day. If, again, the warm currents of tlie 

 North Pacific were to be stopped, the northern hemisphere would be 

 subjected to an entire glaciation. The fossils of the Palaeozoic age 

 seem to indicate a uniform mild or temperate condition of climate, 

 but not so in the succeeding Carboniferous age, which shows signs 

 of reaction. The late Mr. Godwin Austin found large angular 

 blocks in the carboniferous strata of France, which could only be 

 accounted for by referring their inclusion to the agency of ice- 

 carriage, by glacier or iceberg. Large blocks of granite are met 

 with in Scotland in the detrital beds of the coal-basins, which 

 Professor Geikie and other eminent geologists attribute to glacial 

 action. A large block of crystalline rock resembling granite was 

 found embedded in a pit of white chalk near Croydon, and with it 

 were other smaller boulders, all water-worn and composed of a 

 different kind of rock, together with a compact mass of silicious 

 sand derived from the waste of coast line of crystalline rocks, of 

 which there are none 'in the neighbourhood of Croydon. All had 

 sunk together without separating, and must have been firmly 

 held together both during the time that they were floating, and 

 whilst sinking to the bottom of the cretaceous sea. Independent 

 of seasonal changes, circulation between the surface and the sea- 

 depths is aided by the co-operation of heat and gravitation. The 

 Gulf of Mexico, which is not exposed to any cold supply of water 

 from the North Pole, is a perfect reservoir of heat ; further north, 

 close to the shore of Massachusetts, is a cold current running 

 southwards 60 or 80 miles wide. There are thus tAvo currents of 

 different temperatures running side by side in opposite directions 

 and only mingling where their edges impinge upon each other. 

 Again, the Gulf Stream divides itself into several channels, the 

 water of which is warm where the channels are deep, and cold in 

 the shallower channels, occasioned by the water, low in temperature, 

 rising from considerable depths over submarine elevated ridges. 



