488 CUMBHAY (LITTLE). MINERALS. 



weight has not been sufficient to prevent the extrication 

 of air from the fluid mass. Out of many that might be 

 quoted, I shall here add one more instance only of this 

 fact, on account of its locality : the reasons for quoting 

 it will immediately suggest themselves. It is in the rock 

 of Edinburgh castle, in which similar cavities are found 

 sparingly dispersed at a depth of many feet from the 

 surface of the most solid masses. There appears indeed 

 no reason to doubt that the amygdaloids in general bear 

 marks of the same origin, and that the present sub- 

 stances which form their imbedded nodules, have been 

 deposited by secretion or infiltration into cavities, in cases 

 where the loose texture of the rock, and the materials of 

 which it was composed, admitted of such solutions being 

 formed ; a process similar to that by which fissures in 

 limestone and in schist are now daily filled. The examples 

 of this nature on a large scale, formerly described in Rum, 

 illustrate this opinion ; as do numerous others quoted by 

 foreign writers on similar subjects. 



Among the other substances which occur in the amyg- 

 daloidal cavities, are nadelstein and red stilbite ; but they 

 are generally in minute nodules, and require no peculiar 

 notice. 



A more rare substance, which I have not observed any 

 where else except on the adjoining coast, is an indurated 

 steatite. It is sometimes found in nodules as large as a 

 pea ; more frequently they are of a smaller size. Their 

 colour is green, varying from a pale greyish tone to a 

 deep sap-green hue. Occasionally the exterior part of the 

 nodule alone is hard, while the interior is soft and of a 

 paler colour, and in a few instances it contains calca- 

 reous spar in the centre. 



Green earth also occurs among these nodules, present- 

 ing considerable diversities of aspect. It appears a ques- 

 tion yet undecided, whether the green earth of the 

 trap rocks is the same mineral as the chlorite found in 

 the primary strata, or whether even the chlorite of these 



