Prismatic Structure in Sandstone, 8?c. 257 



same rock. The Bass, Traprain Law, and North Berwick Law, 

 are the most conspicuous of these : but many of smaller dimen- 

 sions, scarcely raised above the general surface, occur in other 

 places. It is further obvious, that many of these detached 

 masses of trap are undergoing a rapid decomposition ; gradu- 

 ally mouldering into soil, and leaving exposed, or at least only 

 covered with loose clay and earth, the stratified rocks which 

 they once concealed. 



I have yet to remark, that the general inclinations of the 

 sandstone strata are various, but almost always inconsiderable; 

 and this comprises all that appears necessary to render the 

 geological structure of this district intelligible. 



The strata of the red sandstone, as they appear near Dun- 

 bar, dip to the south-east, or thereabouts, at an angle of nine 

 or ten degrees ; and, in most places along this shore, they 

 present a very consistent regularity. Immediately at the town, 

 however, they are confused and irregular for a small space ; 

 and here also there are intermixed with the red strata some 

 beds of white calcareous sandstones veined with red. 



In u care fully tracing these beds to the pier, where the 

 columnar appearances already mentioned are found, it is easy 

 to see that this mass of prisms is a portion of one of these 

 beds, or that the bed is, in this particular place, divided by a 

 prismatic configuration. The area of the columnar part is 

 such as might be contained in a space of 80 or 100 yards by 

 30; but accuracy in this point is of no consequence: neither 

 is it possible to be obtained, as there is such a gradation from 

 the simple undivided stratum into the prismatic part, that the 

 limits of the latter cannot be fixed. 



It is, indeed, easy to see, on a careful inspection, that the 

 prismatic configuration is assumed by the common sandstone 

 bed in a very gradual manner. The mere indications of an 

 irregular vertical division are first seen ; and these are followed 

 by a definite outline on the surface, making the figure of a 

 prism which is still incapable of being separated from the sur- 

 rounding parts. By degrees, these markings increase, so as 

 to leave hollowed lines in the rocks; and, in a further progress 

 to the perfect structure, the prisms are not only seen to be dis- 

 tinct, but, having been irregularly broken off at unequal altir 



