82 GUOUPS OP ALLIED SPBCIKS [Chap. X 



north as they are at present. Even at this day, if 

 the Malay Archipelago were converted into land, the 

 tropical parts of the Indian Ocean would form a 

 large and perfectly enclosed basin, in which any great 

 group of marine animals might be multiplied; and 

 here they would remain confined, until some of the 

 species became adapted to a cooler climate, and 

 were enable to double the Southern capes of Af- 

 rica or Australia, and thus reach other and distant 

 seas. 



From these considerations, from our ignorance of 

 the geology of other countries beyond the confines of 

 Europe and the United States, and from the revolution 

 in our palaeontological knowledge effected by the dis- 

 coveries of the last dozen years, it seems to me to be 

 about as rash to dogmatize on the succession of organic 

 forms throughout the world, as it would be for a natura- 

 list to land for five minutes on a barren point in Aus- 

 tralia, and then to discuss the number and range of its 

 productions. 



On the sudden Appearance of Groups of allied Species 

 in the lowest known Fossiliferous Strata. 



There is another and allied difficulty, which is much 

 more serious. I allude to the manner in which species 

 belonging to several of the main divisions of the animal 

 kingdom suddenly appear in the lowest known fossili- 

 ferous rocks. Most of the arguments which have con- 

 vinced me that all the existing species of the same group 

 are descended from a single progenitor, apply with 

 equal force to the earliest known species. For in- 

 stance, it cannot be doubted that all the Cambrian and 



