VARIETIES OF PRIMITIVE LIMESTONE. 59 



mended perfectly after freeing the surfaces from carbonate of lime by a weak acid. The 

 cause of these fractures and bendings must be attributed to movements to which the rock 

 containing them has been exposed. There have been, however, but slight movements in the 

 rock indicated, as it occurs in a low ridge, and is not much elevated. It would seem that 

 movements, though slight, are felt by every particle of matter in the rock ; but if it was com- 

 posed of one homogeneous substance, the fractures of such small crystals would scarcely take 

 place in the mass, as they would be supported equally on all sides ; but tlie rock contains a 

 mixture of quartz, feldspar and other hard materials, and the lime being more yielding than 

 these, allows the particles to move on each other, and hence the fractures or bending observ- 

 able in the crystals of the rock. 



Phenomena apparently similar are sometimes observed in prismatic crystals, particularly in 

 the green tourmaline of Chesterfield, Massachusetts. They have apparently suffered a move- 

 ment, but it appears to have been by an imperfect crystallization, or an interference at the 

 time the crystal was in the act of forming. It is not then a true fracture, as in the instances 

 of the Rossie phosphate of lime and zircon, and hence the two phenomena should not be 

 confounded together. 



Recapitulation of the leading facts on the question of the origin of Primitive Limestone. 



1. No instance has fallen under my notice, where this rock appeared divisible into parallel 

 layers like ordinary stratification. The jointed structures, too, are also quite imperfect. The 

 rock is therefore strictly a mass ; it is a whole, or without regular division seams. 



2. Like other unstratified igneous rocks, it appears in the form of veins or dykes, and pro- 

 jects upward through granite and other rocks, in a mode which is inexplicable on any other 

 theory than that of injection from below. 



3. It often underlies granite ; and is so intimately associated with it, as to greatly favor 

 the idea that its origin is connected and cotemporary with that rock. 



4. It has produced, on rocks with which it is in contact, changes which can only be attri- 

 buted to igneous action ; as the obliteration of the granular particles of sandstone, and their 

 reduction to a homogeneous and vitreous condition. 



5. Minerals of the same character, and under the same condition, are found in this rock as 

 in granite : thus, mica enters into the composition of primitive limestone, in a mode quite 

 analogous to that observed in gianitc. 



Rocks which viay be considered varieties of Primitive Limestone. 



1 . Carbonate of Lime and Mica. A mixture composed of these two minerals, occurs in 

 masses sufficiently extensive to be ranked as a rock. Considering the carbonate of lime as 

 the base of the rock, the mica varies in quantity. It occurs at Antwerp in large masses, some 

 of which are composed almost wholly of mica, the carbonate of lime being only in sufficient 

 quantity to hold the mica together. It is in imperfect columns from half an inch to an inch 



