42 GEOLOGY OF THE SECOND DISTRICT. 



" the transition limestone at the Hnc 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 yellowdsh brown mineral resembling some of the 

 varieties of condrodite ; but there arc 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 which 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 hme, 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, througli 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 mehed 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 Umestone. The gradation of change which here exists between the blue and earthy 

 " limestone, and the vvliile crystalline rhombic spar, is distinctly traceable as we approach 



* llEnFlELD's Exploring Visits to the Sources of the Hudson in 1936, p. 1, 2. 



