MINERALOGY OF THE REDHEAD. S6& 



infusible quartz, nor a large empty cavity occupy- 

 ing the centre of the mass. 



The Wernerian hypothesis, which supposes 

 these agates to have been formed by infiltration 

 subsequently to the deposition of the bed, is 

 equally liable to objections. Passing over the 

 difficulty of accounting for the origin of these 

 cells, by the extrication of air from the rock 

 during its formation, we cannot conceive it 

 possible for any flinty solution to have transuded 

 through the pores of the soft bed on its way to 

 fill the empty vesicles, without depositing some 

 siliceous matter in these, and giving to the rock 

 a greater degree of consolidation than it is known 

 to possess. No umbilical cord of agate exists 

 to point out the infiltration opening. And it 

 is no uncommon thing to observe, in the same 

 vesicle, a number of spherical concretions com- 

 posed of concentric coats, and all enveloped in 

 a continuous covering of agate, and surrounded 

 with a crust of green-earth or iron-shot clay. 



These facts, in the history of agate-balls, prove 

 their simultaneous formation with the rock in 

 which they are enclosed. They in this respect re- 

 semble the reniform ironstone which occurs in 

 slate-clay, and the globular masses of flint im- 

 bedded in chalk. These three phenomena have 

 so many points of resemblance, that any theory 

 formed for the explanation of one of them, ought 



