PRIMARY LIMESTONE. 211 



attached to any one of the whole class. It is found in 

 contact with granite in Glen Tilt ; being penetrated, 

 like the accompanying strata, by its veins, and pre- 

 senting consequent changes of character, like those 

 which secondary limestone undergoes when penetrated 

 by trap veins. These consist in the loss of the strati- 

 fied structure, in the intermixture of the accompanying 

 substances, and in a great increase of hardness, attended 

 by a change in the chemical composition. When 

 found in gneiss, in the form of nodules, it is often also 

 penetrated by the same granite veins which intersect^^ 

 that rock ; and, in these cases also, it undergoes cor- 

 responding alterations of character. It is also not 

 unusually found in gneiss, in the stratified form ; as 

 well as in quartz rock and in micaceous schist. When 

 interst ratified with the latter, or with schistose gneiss, 

 it is sometimes so interlaminated with mica as to have 

 been mistaken for these substances by geologists of 

 considerable experience. Rannoch, and Blair in Atholl 

 contain very remarkable examples of these varieties. 

 It is occasionally also found in contact with horn- 

 blende and with actinolite schists ; and, in these cases, 

 it becomes intermingled with those minerals, particu- 

 larly at the planes of contact. It occurs frequently in 

 argillaceous schist, and principally with the fine clay- 

 slate ; either forming masses of considerable extent, 

 or accidental laminae. In these examples also, it is 

 often so minutely interlaminated with that rock as 

 only to be distinguished on the cross fracture ; the 

 laminar one discovering the schist alone with which it 

 is interleaved. It has elsewhere been shown to ac- 

 company chlorite schist in the chlorite series. 



From this enumeration it follows, that instead of 

 occupying any determined place in the order of nature, 

 it is perhaps the most irregular of the whole in its 



P 2 



