Chalk Flints of the Island of Stroma. 161 
clay itself are to be seen on the island now, there are evidences 
of its former presence. But probably it was never of great 
depth, there being no deep valleys or sheltered coves to retain 
it on this small spot of land. Add to this the peculiar form 
of the island, sloping towards the sea on both sides and ends, 
much like the hipped low roof of a house — in some places de- 
scending quite to the level of the beach. Thus, when rising 
on its return voyage, after being submerged and covered with 
the boulder clay, as it slowly lifted up its head from the agi- 
tated waters of the turbulent Pentland, lashed no doubt then 
as now by the waves of the restless " Swelkie"* and " Bores^f 
the softer and lighter portions of the clay were washed out, 
and passed down the sloping sides in muddy streams, and 
were swept away by the furious tides which ran past, the more 
ponderous and weighty materials being left behind. Whence 
the flints came I do not intend to speculate, but merely men- 
tion that many writers upon those found in other parts of 
Scotland point to Denmark and Sweden. My stay on the 
island on this occasion was very short, but this is of little 
consequence, as my son William has since made a thorough 
inspection of the whole island, and finds flints all over. 
The next morning I passed over the Pentland in the midst 
of a storm, with rain and snow, and whilst my horse was feed- 
ing and being got ready for my return home, I took the oppor- 
tunity of looking round John o' Groat's, and there chalk flints 
were to be seen, but not in that abundance as at Stroma. I 
regretted that I could not extend my search further. As the 
subject is worthy of attention, I hope to pursue my investi- 
gations as opportunities ofi'er, for I believe that these flints are 
wide spread, not only in the boulder clays of Caithness, but 
on the surface also. I hope by thus giving publicity to the 
discovery that the attention of others may be called to the 
subject. 
^ " Swelkie " is a whirlpool off the north end of the island, which at times 
is very dangerous. A boat, with seven men in it, was drawn in, and all were 
sucked down and lost. 
t Bores." For instance, off Duncansbay Head the waters rise up all on 
sudden at certain times of the tide into high waves. It is then dangerous for 
vessels and boats to pass through — almost certain destruction to boats. 
