i g6 Dr. Richardson’s Letter on the basaltic Surface 
grassy coat, through which it is only in spots that it shews 
its proper colour ; it is about eight feet thick. 
Sixth Stratum, (/). 
This stratum is composed of rude massive pillars so coarsely 
formed, that on the least abatement of perpendicularity the 
columnar form can scarcely be traced. This stratum is 
about ten feet thick, it forms the vertex of the beautiful 
conical island Beany n Daana, and is marked in the views (/ ). 
These last strata, though they have nothing very remark- 
able in themselves, nor contribute much to the beauty of the 
fa9ade ; yet they exhibit one of the most important facts I am 
acquainted with in natural history, and which, when atten- 
tively considered, throws much light on the nature of the 
operations performed upon our globe since its consolidation, 
and leads us irresistibly to conclusions extraordinary and un- 
expected. 
The fourth, fifth, and sixth strata reach the top of the pre- 
cipice, and vanish together at the waterfall in the north-west 
corner of Portmoon. When they come to the surface, they turn 
inland to the westward in long stony ridges ; these obstruct 
the course of the waters in their descent along the inclined 
plane, formed by the surface of the promontory, and throw 
them over the precipice, in a cascade highly beautiful after 
rain. 
On the facades to the north-west not a trace of them ap- 
pears, these being entirely formed by the lower strata, which 
I have not yet noticed ; but at the distance of a mile, at the 
great depression (already mentioned), the fourth, fifth, and 
sixth strata, with a narrow stripe of the third, suddenly ap- 
