78 THE WONDERS OF GEOLOGY. Lect. I. 



impregnation, and enables them to dissolve a large quantity 

 of calcareous matter." 



36. Marble of Tabreez. — In Persia, a beautiful trans- 

 parent limestone, called Tabreez marble, is formed by 

 deposition from a celebrated spring near Maragha, where 

 the whole process of its formation may be seen. In one 

 part the water is clear; in another dark, muddy, and stag- 

 nant ; in a third it is very thick, and almost black ; while 

 in the last stage it is of a snowy whiteness. The petrifying 

 pools look like frozen water ; a stone thrown on them 

 breaks the crust, and the water exudes through the open- 

 ing ; and in some states the process has proceeded so far as 

 to admit of walking on the surface of the lake. A section 

 of the stony mass resembles an accumulation of sheets of 

 paper, being finely laminated ; and such is the tendency of 

 this water to solidify, that the very bubbles on its surface 

 become hard, as if they had been suddenly arrested, and 

 metamorphosed into stone.* 



37. Stalactites, and Caverns. — By the infiltration 

 of water through limestone rocks, into fissures and cavities, 

 sparry concretions are produced on the roofs, sides, and 

 floors of caverns. The concretionary masses which are 

 dependent from the roof like icicles, are called stalactites; 

 those which form on the floor, from the droppings of the 

 water, are termed stalagmites; and when, as frequently 

 happens, the two unite, a singularly picturesque effect is 

 produced ; the caves appearing as if supported by pillars 

 of great beauty and variety, f Sometimes a linear fissure 

 in the roof, by the direction it gives to the dropping of the 

 lapidifying water, forms a perfectly transparent curtain or 

 partition. A remarkable instance of this kind occurs in a 

 cavern in North America, called Weyer's Cave, which is 

 situated in the limestone range of the Blue Mountains. J 



* Morier's Travels. f Appendix C. X Appendix D. 



