530 PROCEEDINGS OF TKE GEOLOGICAL SOCIETY. [June 6, 



and calcareous wackes. These, as we should expect, are of Tciy 

 limited extent. They never continue any distance, but speedily 

 give way in all directions to metamorphic rocks. The limestone of 

 Craigneil is a remarkable example. The hard and tough nature of 

 this rock has enabled it to withstand denudation better than the 

 more easily wasted conglomerates and altered wackes by which it is 

 surrounded. It rises into a conical hill, the form of which is evi- 

 dently due to glacial action. Although this bed is of considerable 

 thickness, it yet dies out very suddenly along the strike ; and the same 

 appears to be the case with the limestone at Bougang. Of the 

 Craigneil limestone itself not much need be said here, further than 

 that it is a very impure rock, and ought in places to be termed 

 merely calcareous greywacke. It is associated on the south side 

 with schistose serpentine and conglomerate. To the west and east 

 it is replaced by altered, crystalline and amygdaloidal greywackes. 



Association of Serpentine luitJi Calcareoiis Strata. — At Laffin- 

 cleary, serpentine is curiously associated with a highly calcareous 

 wacke and impure limestone. The serpentine occurs as veins and 

 amorphous areas, and is itself veined with carbonate of lime. The 

 calcareous beds have in places assumed the brecciiform structure of 

 Knockdolian rock. On the old raised beach at Whilk, at Bennane 

 Head, at Leffin Knowes, on the farm of Balnowlart, on Knockdolian 

 Hill, in an old quarry at Bougang, at Knockdhu Bridge, and many 

 other places, limestone or calcareous wacke is found abundantly 

 intermingled with magnesian matter, and occasionally passing into 

 serpentine. The rock is generally much confused and broken, the 

 joints being coated with such silicates as steatite, chlorite, ttc. 



These calcareous areas are, as remarked, always of small extent, 

 and occur quite sporadicall}^, often with no apparent relation to each 

 other. But occasionally they seem to follow a certain line corre- 

 sponding to the direction of the strike. Little patches of serpentine, 

 in the same manner, often make their appearance at intervals on a 

 given horizon. Whether these last indicate the former existence of 

 impure magnesian and calcareous wacke's or limestones, like the 

 sporadic beds just referred to, can only be conjectured. 



AYith regard to the former extent of such limestones as those at 

 Craigneil and Bougang not much can be said. Metamorphic action 

 has in all probability considerably reduced their bulk ; but there are 

 good grounds for believing that they never covered any large con- 

 tinuous area, but, on the contrary, were from the first of partial and 

 irregular occurrence. 



YI. COXCLUSIOX. 



In the foregoing general sketch of the phenomena of this inter- 

 esting region, speculations on the probable nature of the agent or 

 agents by whose means the alterations were effected have been pur- 

 posely omitted. It is usually much easier to say what has not 

 caused such changes than to state what has ; but in the present 



will be found in Sir Eoderick Murchison's memoir already referred to. Kide 

 Quart. Journ. Geol. See. toI. vii. p. 154. 



