Limestone. 295 



have produced so great a degree of hardness, and that shining semi- 

 crystalline aspect which the older clay slates exhibit. Now we find 

 the laminae of the clay beds horizontal, or nearly so, and those of 

 the slate highly inclined ; and we trace evidences of a powerful force 

 producing flexures in this rock while in a plastic state. Why not 

 then admit that the agency, by which the strata were elevated and 

 the plastic slate produced, was igneous ? And then we can easily 

 conceive how the rock should subsequently have been so thoroughly 

 indurated. Especially why hesitate, when the fused matter protru- 

 ded at the time of the elevation of the strata, meets us in almost every 

 district of much extent, in the form of trap, porphyry, sienite, or 

 granite ? 



7. LIMESTONE. 



No rock is more widely diffused in nature, or less liable to be mis- 

 taken, than the carbonate of lime. From alluvial marl to the sac- 

 charine limestones associated with gneiss and mica slate, we find an 

 almost endless variety of this rock ; but in nearly every case a drop 

 of acid will enable a skillful observer to detect it and distinguish 

 it from its associates. A more formidable difficulty has always 

 met the geologist in assigning to the varieties of this rock their true 

 places in the scale of strata. 



Most of the limestone in Massachusetts belongs unquestionably to 

 the oldest varieties of that rock. The newest varieties are the fetid 

 and bituminous, which are associated with the new red sandstone, 

 and which have been already described. I have also given an ac- 

 count of the white compact limestone of Newport, Rhode Island, and 

 the gray limestone of Walpole, with the suggestion that they proba- 

 bly belong to the graywacke series. All the other varieties in the 

 State, I shall describe in this place. And as the localities are rather 

 numerous, and the diversities of composition, structure, and aspect, 

 somewhat great ; I shall, to save repetition, follow a topographical ar- 

 rangement in the description. 



Encrinal Limestone of Bernardston. 



Since the first edition of the first part of my report was published, 

 I have had the satisfaction of discovering organic remains, of the 

 family of encrinites, in the bed of limestone in Bernardston. From 

 the highly crystalline character of most of this rock, I had been led 



