ON THE ALLUVIAL DEPOSITS. 379 



ticcil rocks is unimportant in a geological view, I have 

 formerly shown the interest attached to it when in- 

 volving the bones of animals. The production of tra- 

 vertino, chemically the same, is much more important, 

 from its extent, and for other reasons. If it occurs 

 at Matlock and elsewhere, it is best known in Italy, 

 where it is the present produce of lakes and rivers, as 

 it has been from a period beyond record. Its use in 

 the antient and in the modern buildings of Rome is 

 familiar; as is the great depth of this deposit in many 

 places. I have already shown how the formation of 

 this rock has produced obscurities respecting the loose 

 alluvia of Italy and the volcanic tufos ; while it is 

 easy also to see, how, by the casual superposition of 

 alluvia, or of the matters of volcanoes, on antient tra- 

 vertinos, the latter might be mistaken for an ordinary 

 calcareous stratum ; and how, in particular, confusion 

 has thus arisen respecting organic remains. And if, 

 as is probable, it occurs in many other calcareous 

 countries, while hitherto overlooked, as it had long 

 been in Hungary and in the vicinity of the Black sea, 

 it will be for geologists to enquire, whether they have 

 not sometimes confounded it with their "tertiary for- 

 mations :" while, if now forming in other lakes as well 

 as those of Italy, it may hereafter be mistaken for la- 

 custral deposits of a far higher antiquity. Such a de- 

 posit is indeed, essentially, but the same thing ; and 

 it thus unites the phenomena of the present with 

 those of more distant days. 



I have allotted no chapter to the volcanic rocks; as 

 I have nothing important to say of them beyond that 

 which was said under volcanoes. With this one, the 

 history of the materials of the earth is terminated. 



