ANNUAL ADDRESS, 1873. 

 ON LIMESTONE, 



ITS OCCURRENCE, NATURE, AND ORIGIN. 

 BY THOMAS WARDLE, F.G.S. 



THE rocks which constitute what is termed the earth's 

 crust are conveniently grouped into two great classes 

 those formed in or by the agency of water, and those of 

 igneous or volcanic origin. It is beyond the province of 

 the present address to treat of those great rocks which 

 are the result of subterranean heat, such as basalt, trap, 

 and the various kinds of lava, or of the great mountain 

 masses of metamorphic sedimentary rock which have been 

 so altered by the effects of igneous power and proximity 

 as to lose nearly all trace of their aqueous origin, such 

 as the gneissic, quartzite, and schistose rocks. Rocks of 

 the first-mentioned class, those of aqueous or watery 

 origin, may also be subdivided into two classes those 

 which are of sedimentary origin, and those which have 

 been formed in the deeper waters, mainly out of the 

 reach of sedimentary matter. Sir Charles Lyell divides 

 them into mechanical and chemical deposits. The sedi- 

 mentary rocks are those which are composed of the de- 

 tritus, waste, or wash, more or less worn, of previously 

 formed rocks : they are mere sediments formed into beds 

 of strata by moving water carrying in suspension frag- 



