THE IMPERFECTION OF THE GEOLOGICAL RECORD 291 



period the species were suddenly and simultaneously developed in 

 other quarters of the world. It is almost superfluous to remark 

 that hardly any fossil fish are known from south of the equator; 

 and by running through Pictet's Palaeontology it will be seen that 

 very few species are known from several formations in Europe. 

 Some few families of fish now have a confined range; the teleostean 

 fishes might formerly have had a similarly confined range, and 

 after having been largely developed in some one sea, have spread 

 widely. Nor have we any right to suppose that the seas of the 

 world have always been so freely open from south to 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 enabled to double the southern capes of 

 Africa 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 discoveries 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 naturalist to land for 

 five minutes on a barren point in Australia, and then to discuss the 

 number and range of its productions. 



ON THE SUDDEN APPEARANCE OF GROUPS OF ALLIED SPECIES IN 

 THE LOWEST KNOV^N FOSSILIFEROUS STRATA 



There is another and allied difficulty, which is much more seri- 

 ous. 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 fossiliferous rocks. Most of the arguments which 

 have convinced 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 instance, it cannot be doubted that 

 all the Cambrian and Silurian trilobites are descended from some 

 one crustacean, which must have lived long before the Cambrian 

 age, and which probably differed greatly from any known animal. 

 Some of the most ancient animals, as the Nautilus, Lingula, etc., 

 do not differ much from living species; and it cannot on our theory 

 be supposed, that these old species were the progenitors of all the 

 species belonging to the same groups which have subsequently ap- 

 peared, for they are not in any degree intermediate in character. 



