TRANSITION ROCKS. 113 



been bestowed on bringing it forward *, it cannot be supposed 

 to contain any errors, according to the strict notions of Wer- 

 ner ; and if his pupils find it necessary to introduce any ma- 

 terial alterations, and so to mould it, as to suit their own subse- 

 quent observations, it will no longer be the system of that phi- 

 losopher, — which the arguments in the present paper are alone 

 intended to meet. 



The Transition Series is composed of Limestone, Grauwacke, 

 and Grauwacke-slate, Trap and Flinty-slate. Limestone is pla- 

 ced first, as being the oldest member, and is said to rest im- 

 mediately on the newer clay-slate f. Of this we have no in- 

 stance which I am acquainted with in Scotland, where, indeed, 

 transition-limestone may be considered as rather of rare occur- 

 rence. Grauwacke, and grauwacke-slate are with us the princi- 

 pal members. The first of these is a stone usually of a bluish 

 colour, passing into grey, and sometimes greyish-red ; it is 

 composed of fragments, often of considerable size, but some- 

 times so minute as to be scarcely distinguishable ; these 

 fragments are quartz, clay-slate, flinty-slate, and occasionally 

 jasper, which are agglutinated by a basis of clay-slate, through 

 which minute particles of mica are also sometimes dispersed. 



Grauwacke-slate differs from the fine-grained grauwacke on- 

 ly in its minute stratification, and fissile character ; it bears so 

 strong a resemblance to clay-slate in hand-specimens, that even 

 an experienced eye cannot distinguish it ; in the rock it is not 

 so easily mistaken : it usually alternates with grauwacke, and 

 is often remarkably contorted. Both substances are traversed 

 by quartz veins, which are sometimes of enormous dimen- 

 sions, but generally very minute and abundant. 



Vol. VII. P The 



* Werner, " after the most arduous and long-continued investigation, con- 

 ducted with the most consummate address, discovered the general structure of 

 the crust of the globe,'" &c. Jameson's Mineralogy, vol. m. p. 42. 



•f Jameson's Mineralogy, vol. m. p. 147. 



