31:2 



Outlines of the Mineralogy and Geology 



with^ and forms beds in it^ at Brookliue, Brighton, Newton and 

 Needhara ; and it sometimes passes into Wacke so abruptly, that 



the line of demarkation is perfectly distinct. 



V* The external surface of Greywacke is always Tery much 

 altered ; those ingredients of it, which are most easily decompos- 

 ed by atmospherick exposure are gradually removed ; the Quartz 

 frequently remains projecting from the mass, and by the farther 

 removal of the cementing substance^ this falls out; and hence 

 the Greywacke sometimes presents smooth rounded depressions 

 or cells once occupied by these nodules. 



VL Greywacke is generally one of the most metalliferous 

 rocks, but except some slight traces of Iron, and dendritick im- 

 pressions of Oxide of Manganese^ no metals have been observed 

 ia the Greywacke above described. 



VII. No stratification has been observed in this Greywacke ; it 

 is intersected by many perpendicular and parallel seams which run 

 S. W, and N. E. and are distant from each other from 3 to 10 feet. 



w 



Where the rock is intersected by these seams, its faces are perfectly 

 smooth and the corresponding portions of the nodules are found on 



each Bide, or sometimes the nod 



entirely 



side pro 



from the mass, whilst a corresponding cavity is found in 



the opposite portion : 

 a little separated from 



found by tb 



am 



d the interstice is filled with 



i 



table of Greywacke, whose component parts are mo 



than those in the 



a 



portion 



tables may be 



easily removed from their situation, without fracture of the rock. 

 In some instances, we find the interstice filled by two or more of 



tables 



perpendicular seams are freq 



ted by others, which are horizontal : hence the rock fall 



