INTRODUCTION. 3 



A fifth map is given, showing the lands which arc supposed to be now rising and those now 

 sinking. 



The portion of this latter map which relates to the Northern Hemisphere is di-a^Ti from 

 various sources, but much of it is conjectural and infei-cntial, little being knowai of the greater 

 part of it. The portion relating to the Southern Hemisphere has been chiefly deduced 

 from the data laid down by Mr. Darwin in the map published in his volume on " Coral For- 

 mations." 



Prof. Edward Forbes, in speaking of the Gulf weed in the Atlantic, suggested that it might 

 indicate the spot where land had been submerged, and as botanists are disposed to admit that the 

 S.viiGASsuM BACciFERUM, or Gulf Weed, is only another form of the Sargassum vulgare, which 

 fringes our own coasts, it seemed not an improbable conjecture, and its presence must always 

 be taken into accomit in any speculations on the past changes of the distribution of land 

 and sea. I have, therefore, added a map in which the different Sargassum Seas are laid down. 



I had hoped to have given a seventh general map, illustrative of Dr. Forsehammer's con- 

 clusions regarding the regional distribution of different kinds of sea-water. That gentleman has 

 made this the subject of investigation, and has communicated the results to the Royal Society 

 in a paper on the component parts of sea-water in all quarters of the globe. These results 

 have induced him to divide the sea into sixteen regions, each distinguished by different physical 

 qualities. It will be most interesting to compare how far these correspond with the regional 

 distribution of sea anmials and sea plants. Unfortunately his paper has not yet been published. 

 Before I reach the Fishes I trust that this will have been done, and that I may then be able to 

 give a map showing Dr. Forsehammer's sea-water regions. 



The order in which I shall pass the different anim;ils and plants in review, is that known as the 

 descending order, ^-iz. commencing with Man and going down the scale of Nature, imtil we reach 

 the lowest organisms of animal life. Perhaps the most natural course, when I have reached that 

 stage, would be then to enter on the vegetable kingdom by the lowest Hnks in its scale, which can 

 hardly be distinguished from the like links in the animal kingdom, and to work upwards to the 

 highest. I think on the whole, however, that it will be found more convenient to treat the vegetable 

 kingdom as a parallel series, and deal with it also in the descending order. 



