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SCIENTIFIC INTELLIGENCE. 



GEOLOGY AND MINERALOGY. 



1, On the Question in Natural History, Have Genera, like Spe- 

 cies, Centres of Distribution P By Professor E. Forbes. — A species, 

 according to the I'eceived opinion of naturalists, is an assemblage of 

 individuals related to each other through descent, and derived from 

 an original stock. A genus (using the word in its widest sense), is 

 a natural group of species having certain characters of organization 

 in common, but no relationship of descent. Thus, every dog is an 

 individual of a single species, all the members of which are believed to 

 be descended from an original pair or stock ; and, on the other hand, 

 a fox and a dog are two species of one genus, evidently closely allied, 

 but not derived from a common stock. In like manner, among 

 vegetables, the individuals of the species apple might be cited on the 

 one hand, and the apple and the pear mentioned as two species of 

 one genus on the other. Every apple seed produces an apple plant, 

 and is the product of a similar plant ; but apples cannot produce 

 pears, nor pears apples. Every species, consequent on the relation- 

 ship of its several individuals must occupy, or have occupied, a single 

 area, within which there is some point or centre where the species 

 had its origin. The researches of Professer E. Forbes have shewn, 

 that in numerous cases where large assemblages of species, both of 

 plants and animals, appeared to occupy more than one area or 

 centre, the application of geological research to the elucidation of 

 problems of distribution, went to prove that such were only so many 

 parts of a common area, broken up by physical changes in the course 

 of geological time. The researches of zoologists, botanists, and 

 paleontologists, have all tended to shew, that in very numerous in- 

 stances, probably in the majority of cases, natural groups of species 

 {i. e. genera), of various degrees of limitation, occupied definite areas 

 in geological time and geographical space. The assemblage of all 

 the members of one great natural group of monkeys in the old world, 

 and of all those of the other in the new — and in like manner the 

 distribution of marsupials — were quoted to shew that such arrange- 

 ment did not depend on mere elemental condition. Numerous instances 

 cited from amongst both animals and plants, proved that such was 

 the case also in minor groups. The distribution of the genera eden- 

 tata and the camels, of those of the violets and hyacinths, was cited 

 in illustration of the limitations of generic areas. In time we find 

 similar phenomena, of which numerous instances among fossil fishes 

 and niolhisca were mentioned, all tending to shew, that when the 

 species of a geims once appeared, they either continued, or new forms 

 of the same group were added to or replaced thorn, until the genus 

 ceased to have representatives ; so tliat each genus might be said to 



