210 PRIMARY LIMESTONE. 



this, and probably in any country, in a regularly stra- 

 tified disposition, it forms either a limited series of 

 beds, alternating with one or more of the various 

 strata, or else occurs in single ones of very small 

 extent: while, in other cases, and more rarely, it con- 

 sists of irregular nodules of different sizes, possessing 

 no marks of stratification. 



The larger collections of beds preserve the usual 

 parallelism to the surrounding strata ; being some- 

 times repeated in succession, at others, alternating 

 with smaller or larger strata of the accompanying 

 rocks. The smaller beds rarely continue for any con- 

 siderable space; being extenuated till they vanish, 

 after a short course ; while often consisting of little 

 more than a single thin stratum, or of a few detached 

 ones, alternating with the including rock. In either 

 case, they sometimes occupy a considerable space 

 according to their breadth, without being far prolonged 

 lengthwise ; thus forming irregular insulated tracts. 

 Not unfrequently also they vanish and again appear, 

 even at distances of many miles, with unaltered cha- 

 racters, and accompanied by the same strata ; as 

 happens, remarkably, in that long range in which the 

 limestone of Glen Tilt is comprised. In these cases, 

 when the angles of elevation are also liigh, they dis- 

 play that character of far prolonged and narrow lines, 

 to which the term vein has, not unnaturally, been 

 applied by the people. The nodules or masses which 

 possess no marks of stratification, rarely attain a di- 

 mension exceeding a few hundred yards; and this 

 particular mode of disposition occurs most frequently 

 in association with gneiss. 



Primary limestone accompanies every rock, and al- 

 ternates with every member of the associated strata ; 

 nor does it appear, in this country, to be peculiarly 



