168 TALCOSE SCHIST. 



own chlorite schist is no rule for others ; though I 

 may observe, that in Ben Lawers, it abounds in Tita- 

 nite, where it is traversed by quartz veins. Its other 

 uses may be compared with those of micaceous schist : 

 being quarried for roofing slate in Argyllshire, though 

 inferior even to the worst varieties of argillaceous schist. 



Tulcose Schist. 



If Talc be substituted for mica or chlorite, the de- 

 finition of talcose schist is the same as that of the 

 preceding two ; but as it occasionally graduates into 

 both, it cannot always be decidedly distinguished from 

 them. As far as I have observed, it is always very 

 limited in quantity, and of comparatively rare occur- 

 rence. Resembling micaceous schist in its general 

 aspect, it is disposed in similar irregular beds where 

 it occurs, but is as yet only known to me as forming 

 portions of the general masses of gneiss, chlorite schist, 

 or micaceous schist, or as being peculiarly connected 

 with Serpentine. 



Where in company with gneiss, it is commonly at- 

 tended by chlorite or micaceous schist, or both, form- 

 ing a sort of intermedium by which it is connected 

 with the principal rock. The strata are, generally, 

 exceedingly limited in all their dimensions ; and if 

 occasionally thick in some parts, yet they become 

 soon extenuated till they disappear. Where associ- 

 ated with micaceous or chlorite schist, it passes into 

 both of these by imperceptible gradations ; as might 

 be expected from the affinity existing among the 

 three minerals respectively characteristic of these dif- 

 ferent rocks. In these situations also it is always in 

 very small quantity ; at times indeed so very minute,, 

 as to occupy only an occasional lamina in the general 

 mass. Even then, its natural affinity to serpentine 



