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 connected 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¬ 
connected 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 
fusion, 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 this rock, and of their peculiar rela¬ 
tions, I remark, that the occurrence of graphite 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 whieh 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 limestones. At the first thought, it may 
not appear in point; but when it is compared with the result wdiich always occurs in furnaces 
when in good action, it certainly becomes important. The fact which I deem the most im¬ 
portant, is its production by 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 we'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 they are in 
good action, appearing among the cinders and slags.at the clearing of the furnaee. 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 graphite, I have the pleasure 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 great excess, strongly imply that it has been 
New-York Geological Report for the Second District, 1838, p. 202. 
