1866.] J. GEIKIE — CAHEICK, ATR3HIEE. 515 



line of strike (S.W. to N.E.), terminates at Pinmore Bridge on the 

 river Stinchar, where it is cut off by another fault coming from 

 the west. 



The metamorphic rocks usually dip at a high angle, while the 

 strike corresponds in a remarkable degree with that of the unaltered 

 strata of the surrounding country. On the Survey-maps we have 

 distinguished three great groups of rocks, viz. Felstones, Diorites, 

 Serjyentines. 



Felspathic rocks are by far the most abundant, and are very 

 varied in structure and aspect. The diorites and serpentines, on 

 the other hand, have a more definite character, and are usually 

 interbedded or very closely associated. It is worth noting, that, if 

 we traverse the strata from south to north, we shall find that inter- 

 bedded diorites and serpentines alternate with great belts of felspa- 

 thic rock. Thus, starting from the fault which forms the southern 

 boundary of the metamorphic rocks, we first cross amygdaloidal, 

 finely crystaUine, and brecciiform felspathic rocks. Thereafter, as at 

 Balhamie Hill, we come upon serpentine with associated diorites. 

 Leaving Balhamie Hill, we again pass over a belt of felspathic rocks, 

 until, at Carleton Hill and Lendalfoot, we find ourselves once more 

 among diorites and serpentines, and so on with the beds to the north. 



The bounding fault on the south unfortunately throws some doubt 

 on the relation which the metamorphic rocks bear to the unaltered 

 strata. But, notwithstanding the south-east dip of the latter, the 

 downthrow is to the north ; and therefore the metamorphic strata 

 must occupy a somewhat higher horizon than the unaltered wackes 

 against which they abut. Little isolated portions of metamorphosed 

 rock are met with here and there among the unaltered grey wackes 

 alluded to, often far removed from the chief area of metamorphic 

 strata ; but an account of their probable origin and connexion with 

 strata denuded away is reserved for a forthcoming memoir of the 

 Geological Survey. Several areas of unaltered strata, enclosed and 

 surrounded on all sides by metamorphic rocks, will be described 

 below as representing the nature of the beds which haye become 

 metamorphosed. The unaltered strata of this region exhibit the 

 usual character of the Lower Sihman greywackes and shales of the 

 southern uplands of Scotland. They are all strongly felspathic, 

 but are usually more highly impregnated with alkahne matter than 

 the Siluiian rocks of Berwickshire, Peeblesshire, Selkirkshire, and 

 other districts which have been examined by the Survey. Many 

 of the beds eff'ervesce freely with acids, showing the presence 

 of lime, while the abundance of magnesian matter has often tinged 

 the rocks with green. Immediately south of the metamorphic region, 

 the unaltered Silurian strata are not markedly magnesian, but they 

 still contain in places a not inconsiderable admixture of calcareous 

 matter. 



At present attention is directed to a generalized description of 

 the metamorphic strata, for the purpose of tracing the various 

 stages in the process of alteration, and of thereby attaining to some 

 knowledge of the causes which have induced metamorphism. 



