Diallage Rock of Shetland. 105 



the country, it will be found that the protuberant masses above- 

 mentioned, are disposed in lines or interrupted ridges, which 

 are parallel to the general direction of the neighbouring strata, 

 or to the common tendency of all the stratified rocks of the 

 country ; that is, to the eastward of north. On the low shores 

 also, it will be seen that all the points projecting into the sea, 

 which are formed of the diallage rock, preserve the general 

 bearing in question ; being divided from each other by narrow 

 creeks, corresponding to those parts of the surface where the 

 rock does not rise above the soil. 



Another indication of the stratified disposition of this rock is 

 found in its regular juxtaposition to the strata of gneiss, mica- 

 ceous schist, or argillaceous schist, which it follows ; and that 

 is still more strongly evinced by its occasional alternation with 

 beds of these rocks of different dimensions, often of very con- 

 siderable magnitude. The small elevation to which it rises 

 above the soil in the interior, and the lowness of the rugged 

 shores where it is laid bare by the sea, almost always prevent 

 the observer from satisfying himself respecting the stratified 

 disposition of this rock, by the unquestionable evidence of the 

 forms of the beds and their divisions ; and, in the high cliffs, 

 where he might expect to find them distinctly displayed, they 

 are rendered obscure by the innumerable fissures in all direc- 

 tions, already mentioned, by which the divisions between the 

 beds are confounded. But in the small island of Houna, which 

 lies between Balta and Unst, the stratification is perfectly dis- 

 tinct ; not only the direction but the dip of the beds being 

 easily traced, and their dimensions also admitting of measure- 

 ment. In Fedeland point also, where thin beds of diallage 

 rock are interposed among those of the other primary schistose 

 substances, there is no difficulty in tracing their regularly stra- 

 tified disposition. 



Having thus proved that diallage rock is stratified, it remains 

 to point out the rocks with which it is here associated, and the 

 place which it must consequently hold in the system of succes- 

 sion among these. 



In some places it is in immediate contact with extensive bodicit 



