GEOLOGICAL CONCLUSIONS. ?,()?, 



through the middle of the two oceans, the Pacific and Atlan- 

 tic, is near the parallel of 27° or 28°, or one-half nearer the 

 equator than the parallel of 55°. It is difficult to account for 

 an oceanic temperature high enough to give England's seas 

 68° F. as the average for the coldest winter month, even sup- 

 posing the Gulf Stream to have aided ; but it is vastly more 

 difficult if no such northeastward current existed, and the high 

 temperature extended equably so far from the equator. The 

 probability is therefore strong that the existence of coral reefs 

 iu the Oolitic era in England was owing to the extension, by 

 the aid of the Gulf stream, of the isocryme of 68° mo\*e than 

 30° in latitude (and over 3,000 miles in distance) beyond its 

 present most extra- tropical position, just outside of the Ber- 

 mudas ; in other words, that the whole ocean was just enough 

 warmer, to allow of this oceanic current (part of the great 

 water-circulation of the globe) to bear the heat required for 

 corals as far north as northern England. 



The present isocryme of 44° F., as drawn on the chart of 

 the world accompanying this volume, has approximately the 

 course which that of 68° F. probably had in Oolitic times. It 

 should have a little less northing, and the loop to the north 

 should lean more to the eastward. The latter would have been 

 a consequence of the submerged condition at the time of most 

 of the European continent. 



The ocean's waters seem to have cooled somewhat before 

 the next period — the Cretaceous — began, since evidence fails 

 of any Cretaceous coral reefs in the British seas ; but such 

 reefs prevailed then in central and southern Europe, so that 

 the amount of cooling in the interval since the Oolitic era, 

 had not been large ; and as late as the Miocene Tertiary, there 

 were reef corals in the seas of Northern Italy, above latitude 

 45° N., or that of Montreal, in Canada. 



