IGNEOUS ORIGIN OF I,II\IESTONE. 53 



I shall now leave that class of phenomena which 1 have been so long pursuing ; and which, 

 if it is proper so to say, appear to nie to furnish conclusive evidence of the proposition early 

 advanced, that limestone, under some circumstances, is an igneous rock. 



At my last visit to Theresa fails, in the summer of 1841, while examining the disturbed 

 beds of Potsdam sandstone, I discovered a mass of coarse yellowish crystalline limestone 

 immediately beneath them. On uncovering the lowest layers of sandstone, I found that 

 thcv w'ere not only vitreous, but were somewhat vesicular. The cavities were angular ; and 

 some contained, as it appeared, small masses of limestone : these had disintegrated and fallen 

 out, leaving small irregular spaces. The thickness of the altered portion appeared to be 

 from eight to twelve inches, and might be more, as I was not prepared to uncover the lower 

 portion of the sandstone where those chanscs were observed. The color of the altered mass 

 is a deep brown, without a vestige of the granular structure which appears in the rock only a 

 few feet above. The line of demarcation between the sandstone and limestone is quite dis- 

 tinct, but is an irregular line similar to the diagram No. 17, where the lower half of the sketch 

 marks the position of the limestone and the irregular line of contact, and the upper, the 

 sandstone. 



a. Limestone, b Altered sandstone, c. Sandstone. 



That there is an alteration of this rock, few will question on an examination of the speci- 

 mens in the State collection, and more especially after an examination of the rock in place. 

 There is, in my opinion, nothing in this case so conclusive as the appearance of the sandstone ; 

 it has not passed into the state which is perfectly vitreous, like milky quartz, but is still in- 

 termediate between sandstone and that clear vitreous quartz of the common varieties of 

 granite. It is much deeper colored than the common mass of sandstone at this village ; and 

 the process to which it has been subjected has given it toughness, and a greater solidity. All 

 these facts, together with its numerous pores, go to show a remarkable change ; and inasmuch 

 as the changed portion is in contact with limestone, the inference does not seem to be too far 

 fetched, to attribute those changes to the limestone. Besides, I was unable to discover any 

 other rock at the place, either granite, trap or serpentine, which are usually considered as 

 igneous products. At the village of Dekalb, I discovered masses of limestone in 1837, which 

 also appeared to have been an altered sandstone. Wherever those changes appear in the 

 structure of the sandstone, the rocks have been tilted u]) ; an important fact, when taken in 

 connection with the other facts. They all seem to corroborate each other, and conspire to 

 prove the great fact in relation to the limestone, that it is one of those original constituents of 

 the earth which forms the deeper seated part of the crust, and like granite, has been always 



