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primary ones in some places, and conformable in 

 Others ; as the varying positions of these determine 

 those two relations. 



In its depth, this rock presents an infinite variety ; 

 the mass of strata heing either originally thin, or else 

 attenuated in some places, till it disappears, while in 

 others, it amounts to many hundred yards in thickness. 

 This attenuation might be presumed from general 

 experience and principles, were there no evidence of 

 it ; since the persistence of strata is imaginary, and 

 all have their limits ; disappearing in their lateral pro- 

 gress, sometimes not to recur again for a considerable 

 space. 



If examples of these variations are required, Loch 

 Greinord presents a case where this sandstone nearly 

 disappears between the gneiss and the superincumbent 

 strata ; as instances of the reverse are seen in Arran, 

 Caithness, Shetland, Rossshire, &c., where they range 

 from some hundreds to three thousand feet, or more, 

 in thickness. The dimensions of the individual strata 

 are also various ; the conglomerate beds being com- 

 monly the thickest, as the fine ones are the reverse ; 

 "though the former are sometimes divided into distinct 

 strata by finer sandstones. When not thus separated, 

 as is most common, they often attain the depth of a 

 hundred feet or upwards, without a division ; while 

 the fine sandstones vary from a few yards to as many 

 feet, and even to less than an inch in thickness ; when 

 they consequently assume a schistose character. In 

 these cases, the divisions of the beds sometimes result 

 from a change of texture or composition, at others, 

 from the intervention of mica, or clays of different 

 characters, or shales, or argillo-calcareous compounds. 



Viewing this sandstone as a single geological de- 

 posit, or group, extending from the primary strata to 



