140 GEOLOGY AND PALEONTOLOGY. 



DEVONIAN AND SILURIAN FORMATIONS. 



The specimens referrible to strata of this age are few, and these are in such condition as to 

 give little satisfactory information regarding the rocks in place. 



NEWER IGNEOUS AND METAMORPHIC ROCKS. 



Igneous and metamorphic rocks of the Limpia, Guadaloupe, and Organ mountains, Sierra 

 Madre, etc., which are of modern origin.* 



OLDER METAMORPHIC ROCKS. 



Metamorphic rocks of Silurian and Devonian age, forming the range of the Cordilleras and 

 the isolated mountains in the great plain on the east of that mountain chain. 



* The materials which appear as the result of igneous and metamorphic action, may be derived from rocks of the coal 

 measures and from older formations, as well as from those of more recent date. But from all we know of the character of 

 metamorphic, silurian, devonian, and carboniferous strata elsewhere, those here referred to do not possess the same characters 

 and do not belong to the same period of metamorphism. 



