IGNEOUS ORIGIN OF LIMESTONE. 55 



ing the mass. In general, there is no similarity in the limestone to the latter class of rocks. 

 There are still some phenomena which are inexplicable on any other hypothesis than the one 

 which maintains a previous state of fusion, and which left in some instances oval cavities 

 precisely similar to those so abundant in amygdaloid. These cavities not appearing in the 

 rock itself, but in the simple minerals of the rock, will come up for observation in another 

 place. 



I conceive that minerals, when they exist in veins in a rock, or in segregations, are posterior 

 in their formation to the rock itself, and may have been formed in various ways ; but they can 

 not be supposed to be comiected in any way with the state in which the rock may have been 

 in a time anterior to their production. But when they occur disseminated through the mass, 

 and surrounded on all sides by homogeneous particles of which the rock is formed, and dis- 

 comiected wholly with cavities, seams or veins, we are necessitated by the facts and condi- 

 tions of the case to suppose, at the time of their formation, a perfect mobility of the particles 

 composing the rock, and we have two suppositions to make : one, that the mobility of the 

 parts was by aqueous solution, aided perhaps by caloric ; and the other, that of igneous 

 ifusion, and we are to adopt that view which best comports with our present knowledge of the 

 agents and powers of nature concerned in their production. 



Leaving out of view the presence of other minerals in tliis rock, and of their peculiar rela- 

 tions, I remark, that the occurrence of gi-aphite is the one most decisive in the question under 

 consideration. This view of the subject was taken in the Report for 1838, in the following 

 words : "In relation to the primitive limestone, there is one fact which I deem worthy of 

 notice, and which, it appears to me, has a bearing on the question under discussion : it is the 

 presence of foliated plumbago in all the primitive Hmestones. At the first thought, it may 

 not appear in point ; but when it is compared with the result which always occurs in furnaces 

 when in good action, it certainly becomes important. The fact which I deem the most im-: 

 portant, is its production b}^ heat, in those cases where the elements of the material are 

 present; and we have no account of its formation, except in those instances where wc have 

 good evidence that igneous action has been concerned. Thus, in no instance do we find it 

 imbedded in sedimentary rocks ; but in furnaces, it is produced abundantly when thej^ are in 

 good action, appearing among the cinders and slags at the clearing of the furnace. This sub- 

 stance is made in the greatest quantity when the heat attains its maximum state, but never 

 while it is below a certain temperature."* 



In support of the view here taken of the origin of gi'ai)hite, I have the ])leasurc of seeing 

 that Prof. Rodgers has recently adopted a similar opinion in his Report of New-Jersey, from 

 which I shall take the liberty of transcribing several passages relating to this subject. " The 

 " invariable occurrence of the graphite in portions of the altered belt remotest from the dyke, 

 " and Its never existing in more than a trivial quantity even adjacent to the vein, when the other 

 " extraneous minerals are frequently present in gi-eat excess, strongly imply that it has been 



♦ KewYurt Geological Report for the Second Duslnct, 1833, p. 202. 



