42 
GEOLOGY OF THE SECOND DISTRICT. 
“ the transition limestone at the line of contact; the latter being here converted into white 
“ masses, remarkably crystalline in their structure, and interspersed with scales of plumbago.”* 
The mass of limestone spoken of by Mr. Redfield, at Port Henry, is another instance of this 
rock being enclosed in the primary. On one side it is a very pure carbonate of lime, contain¬ 
ing small masses of sulphuret of iron, and a yellowish brown mineral resembling some of the 
varieties of condrodite ; but there are no gradual changes in the rock to a blue limestone. On 
the other side it becomes a variegated limestone, mixed very plentifully with serpentine, as- 
bestus, etc. 
I should leave the subject in an imperfect state, were I to omit the opinion of Prof. Henry 
D. Rodgers, of Philadelphia, who has expressed an opinion entirely on the side of those who 
support the metamorphic theory; and in his Final Report on the Geology of New-Jersey, 
he has given in detail his views of the whole subject, which he has illustrated by a remark¬ 
able example about four miles southwest from Sparta, at the southeast base of Pimple hill. 
The whole argument is of sufficient interest to be transcribed. “ Between three and four 
“ miles southwest from Sparta, on the northwest side of a low ridge of gneiss, we find a very 
“ interesting locality of altered limestone very nearly in the prolongation of the belt which 
“ passes along the southeast base of Pimple hill. This spot is remarkable, less for the extent 
“ or breadth over which the limestone has been affected by igneous action, than for the strik- 
“ ingly convincing evidence which it affords of the nature of the changes induced in a calca- 
“ reous rock by the series of igneous veins and dykes which we have been tracing. The 
“ ridge itself, along the side of Avhich the limestone has been altered, consists chiefly of a 
“ thinly-bedded micaceous gneiss. Through the summit, or rather on the northwestern flank, 
“ which is often abrupt and rugged, there rises a thick granitic dyke, a vein of very hetero- 
“ geneous composition, supporting the steeply-dipping beds of gneiss, whose usual inclination 
“ is at an angle of 80 ° to the southeast. The vein, though various in character, and some- 
“ what difficult to describe, owing to the imperfectly developed nature of its minerals and 
“ their complete interfusion, may be characterized as consisting, in the main, of mica in large 
“ excess, quartz, carbonate of lime, feldspar and augite. It contains spinelle, sapphire and 
“ green talc, besides several other minerals less distinctly crystallized. When we consider 
“ the highly micaceous character of the adjacent gneiss rock, through which the matter of 
“ the vein must have passed in reaching the surface, and the abundance of mica, especially 
“ of the brilliant golden variety, found so plentifully, not only in it, but in the adjacent parts 
“ of the altered limestone, we cannot resist the impression, that a portion of the primary 
“ strata along the sides of the dyke have been melted and incorporated into it, floating, in 
“ combination with the other materials, to the surface. Immediately upon the western side 
“ of this curious vein, and ranging along the base of the hill, occurs the narrow belt of al- 
“ tered limestone. The gradation of change which here exists between the blue and earthy 
“ limestone, and the white crystalline rhombic spar, is distinctly traceable as we approach 
Redfield’s Exploring Visihs to the Sources of the Hudson in 183G, p. 1,2. 
