364 



MINERALOGY OF THE REDHEAD. 



The Structure of this bed of amygdaloid, leads 

 to the conclusion, that while a general disposition 

 to stratification prevailed in the aqueous menstruum, 

 there existed a number of partial spheres of aggre- 

 gation. Thus, while one portion of the fluid was 

 depositing grains of calcareous-spar and quartz, and 

 enclosing these with wacke, claystone or felspar ; 

 another portion was depositing basalt, clinkstone 

 and greenstone, together with nodules of flint, 

 jasper, and calcedony, in the form of agate-balls. 



It appears evident from, simple inspection, that 

 these agates must have formed a part of the ori- 

 ginal composition of the rock, as the vesicles in 

 which they occur, are in many places so nume- 

 rous, that if empty, the rock could not sustain it^ 

 own weight, much less the pressure of the super- 

 incumbent strata. Had these agates acquired their 

 form and structure from fusion by means of heat, 

 the soft clay which often encloses them, and in 

 many cases fills a portion of the same cavity, must 

 have been melted at the same time, and the friable 

 enclosing rock would now have exhibited in it^ 

 superior induration some of the marks of ig- 

 neous influence ; yet the clay continues loosely 

 aggregated, and the enclosing rock, even where in 

 contact with the agate,* can be scratched with the 

 nail. Besides, had these balls of agate ever been 

 in fusion, we could not have expected to find, as 

 we frequently observe, the fusible crystals of car- 

 bonate of lime im.pressing their form on the alnaost 



