1615.] Transactions of the Geological Sociehj, roL 11. 447 



which constitute the surface of the earth ; and till it is confined to 

 this, it can never become a useful nor correct science. If you 

 can demonstrate by petrifactions the epochs of the formation of 

 rocks, or the changes they must have undergone, do so; but never 

 reason or speculate from tlie mere love of hypothesis. 



I may just observe for the consideiallun of Dr. M., that nothing 

 is more common than to find sand-stone having exactly the struc- 

 ture of his Cornish granite, 1 mean decaying ultimately into balls. 

 As examples, I may mention a sand-stone in the Isle of Skye, a 

 sand-stone in Fifeshire, and another in Dumfries-shire. It fol- 

 lows, therefore, that if the Doctor's reasoning about the igneous 

 origin of granite be accurate, he must admit likewise the igneous 

 origin of sand-stone. 



IV. Notes . on the Mineralogy of the Neighbourhood of St. 

 David's Pembrokeslme. By John Kidd, M. D. Prof. Chem. in 

 the University of Oxford, M. G. S. — It would appear from Dr. 

 Kidd's description, that the fundamental rock of this district 

 is a syenite, which seems in some cases to pass into granite, in 

 others to porphyry; but, unfortunately, the descriptions are not 

 sufficiently minute to make us sure of these transitions. Beds or 

 rocks of these three different species, however, occur here. Over 

 the syenite, and, in general, covering the flat country, lie beds of 

 elay-slate, which vary a good deal in their appearance. This slate 

 is often black, has little lustre, and contains quartz veins running 

 through it ; hence it is probably a transition slate. Dr. Kidd calls 

 it grey-wacke ; but tliat term never can be applied correctly to a 

 slate. Indeed it is quite obvious from Dr. Kidd's observations, 

 that the term grey-ivacke has no fixed meaning in his mind : yet it 

 is as well defined a rock as any other, and any mineralogist in five 

 minutes might make himself so well acquainted with its charac- 

 ters, as afterwards to run no risk of confounding it with any other. 

 The following definition may be of some use. 



" Grey-wacke of Werner is a conglomerated rock with a basis 

 of clay-slate. It contains portions or fragments of clay-slate, 

 flinty-slate, quartz ; and sometimes grains of felspar and scales of 

 mica." 



If Dr. Kidd dislikes the term grey-wacke, he may substitute 

 transition sand-stone. The word grey-wacke was invented by the 

 miners at Freyberg, wliere the rock abounds. Werner adopted it 

 from tliem, and drew up an accurate description of tlie rock. 

 Very good specimens of it arc to be found in the Pentlands and 

 Lamermuirs, near Edinljurgh. About 100 yards ea^it of the fourth 

 milestone from Truro in Cornwall, there is a quarry of excellent 

 grey-wacke, wliicli is employed in mending the road. JNIany 

 other Biitisli locidities ml^ht be given; but from cither of these 

 two it would be easy to Ijring uj) a suflicicnt nuniber of specimens 

 to London, to make every iniiifraloglst familiar with the appcar- 

 U)ce of this rock. I conceive that the structure of the country 

 described iit this paper by i)r. Kidd is similar to that of the 



