Murchisoris Silurian System. 



235 



felspar, hornblende, and iron pyrites, with a little dissemi- 

 nated lime alternate with flags, containing Asaphus Buchii, 

 and other trilobites of the lowest beds of Silurian rocks. The 

 beds of volcanic and sedimentary rocks are conformable, one 

 above the other, indicating so many distinct alternations of 

 volcanic and sedimentary deposit. From evidence of this 

 nature, Mr. Murchison has shewn, that submarine volcanic 

 eruptions were frequent during the formation of the lower 

 Silurian beds, while the upper Silurian rocks and old red 

 sandstone were formed during a long period of tranquillity, 

 after which, these last deposits were dismembered and 

 thrown up by vast outbursts of intrusive trap. Mr. Murchi- 

 son is further led to the conclusion, that the carboniferous 

 system was deposited in vallies after the older strata had 

 been upheaved, and that subsequent dislocations, including 

 some of the most violent with which we are acquainted, took 

 place after the accumulation of the coal measures and 

 lower new red sandstone. How far these conclusions may 

 be borne out, or modified by the observations of geologists 

 in other parts of the world, we are not yet prepared to say ; 

 but we feel strongly impressed with their general accuracy 

 in regard to geological facts in India. 



The following examples of the dislocations of Silurian 

 rocks in Wales, are given by Mr. Murchison. The first is a 

 complicated fault by which a mass of Aymestry limestone(c) 



has been thrown into nearly vertical position abutting against 

 the edges of a mass of similar limestone, which has been thrust 

 up between the highly inclined strata and another dislocat- 

 ed mass. Each of these bands of limestone (c) is capped 



