36 GEOLOGY. 



surrounded and separated by valleys and passes clothed with abundant 

 vegetation. The decay of the projecting limestone leaves little soil 

 behind, since most of the rock is soluble, and the little which is formed 

 is promptly carried away by wind and rain. 



In the eastern Alpine region there are large and more or less indi- 

 vidual bodies or " reefs" of dolomite, and sometimes of limestone, 

 which possesses exceptional characteristics. They are essentially 

 without stratification, are poor in fossils, have steep slopes, and a 

 superficial bedding concentric with the surface. As the steep slopes 

 suggest, these reefs wedge out rapidly on some or all sides. These 

 bodies of dolomite (or limestone) attain great thicknesses, and are 

 associated sometimes with thinner beds of stratified limestone or 

 dolomite of a composition like their own, and sometimes with beds 

 of clastic rock which fit up against them on some or all sides. From 

 the reefs, there are often projections of dolomite extending out into 

 the clay-beds surrounding. 



In spite of the difficulties involved in the explanation, it is very 

 generally believed that the so-called reefs are really such, and probably 

 of coral origin. The absence of abundant fossil corals in them seems 

 at first a difficulty; but corals are the most abundant fossils found, 

 and the absence of recognizable coral structure in the body of some 

 modern coral reefs is well known. Coral is one of the most soluble 

 forms of CaC0 3 , and is therefore more readily subject to change than 

 most other organic deposits of this substance. Coral reefs are known 

 to possess the superficial concentric stratification which character- 

 izes these reefs, and to possess similar lateral projections. On the 

 whole, the structure of the dolomite reefs seems more readily explained 

 on the coral reef hypothesis than on any other. In the making of the 

 limestone of the alpine phases of the system, marine algae appear to 

 have played an important part, and even the reefs have been ascribed 

 to them. 



The Trias of the Italian Alps is the source of the Carrara marble. 

 The Trias of the western Alps is largely non-marine. In some parts 

 of Switzerland, the Upper Trias contains coal, and contemporaneous 

 igneous rocks enter into the same division of the system. 



The marine phase of the system shows that the physical conditions 

 which obtained in southern Europe, where there was an open sea, were 

 notably unlike those of western and northwestern parts of the continent 



