[Footnote 5: We have not unfrequently noticed, both in the writings and conversation of some geologists, a disposition to sneer at the subsidiary branches of natural history. Mineralogy and conchology, are light and mean in their estimation, when compared with the study of extensive strata and ponderous boulders. Like Irving's testy governor of Manahatta, who settled the accounts of his clients by placing their books in the opposite scales of a balance, they decide on the value of a science, by the absolute weight of the objects embraced by it. Geology, as well as any other branch of natural history, may degenerate into a mere love for the curious, or have for its principal aim, the perfection or improvement of some ideal system of classification, without advancing a single step further.] Another curious _geological fact_ appears to be established more especially by fossil trilobites; it is that precisely the same species of animal relic, is the most generally diffused over the globe, in proportion to the antiquity of the rock which contains it. Thus the transition limestone of England, France, Germany and Sweden, contains the species called the Calymene of Blumenbach, in common with the same formation which extends over so large a portion of the United States. Different genera and species of the trilobite are now found in almost every part of the globe, and are frequently exceedingly abundant in the rocks which contain them. That they must have swarmed in particular places, is abundantly evident from a number of localities in our own country,--millions, for example, must have lived and died not far from Trenton falls, in the State of New York. There are very few of the numerous visiters to that romantic cascade, whose curiosity is not awaked, by the multitude of these petrified beings, seemingly of another world, which are there entombed. Although many parts of the trilobite are now found distributed through the rocks which contain them, in such a manner as to lead to the conclusion, that they were separated by decomposition, after the death of the animal; yet the perfect preservation of others, and the rolled and disjointed attitudes which we should expect such creatures to assume when disturbed, lead to the conjecture, that they have been often suddenly destroyed, and as suddenly enveloped in that earthy matter, which afterwards became an indurated rock; thus preventing the separation of the harder parts, by the slow process of decomposition.[6] [Footnote 6: Vide De la Beche's Geological Manual.]