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A DEPOSIT OF DIATOMACEOUS EARTH, -SHIRE. 3

III.—On a Deposit of Diatomaceous Earth, near the East End of Loch Leven, Kinross-shire. By J. DUNCAN.

(Read 15th December, 1915.)

ABOUT one mile south of village, between the farm of Lochend and old Gullet Bridge, during excavations in the roadway for a pipe track in connection with the new com­ bined water supply from Glen Farg, a deposit of diatomaceous earth was exposed, extending over 40 yards of the trench. Thin layers of diatomite associated with lake peat were also observed in a continuation of the same trench, near - well, at a point about 100 yards north of Redhouse. The roadway is fully half a mile east of Loch Leven and follows the course named in the old maps as " The Causeway," meaning a pathway across a marsh. This possibly followed a natural elevation, although in wet weather it must have been impass­ able, as the roadway leading to the south of Scotlandwell is carried across a fairly extensive deposit of lake peat. The physical features show that Loch Leven in byegone days must have extended at least two and a half miles eastward beyond its present boundary, Surface conditions, therefore, favoured the idea of the existence of a fairly good deposit of diatomite. Accompanied by Mr D. Tait of H.M. Geological Survey I revisited the locality with the object of proving the extent of the deposit and its relative thickness. We carried out a series of excavations ; one in a field just across the wall from the roadway where the diatomite was first observed, may be given as typical. We found :—

Turf 6 inches. Brownish clay getting lighter towards the bottom . . 6 „ Clay fighter in colour with vertical rootlets, of a dia­ tomaceous nature . . 6 „ Diatomaceous earth . .6 „ Peaty layer . . . . J inch Sand and gravel . . . Thickness unknown.

The conclusions arrived at may be briefly summarised, thus :— The deposit may not extend far to the west from the roadway and does not exceed 50 yards in width and only averages 6 inches in thickness, which is far too thin to be of any economic Downloaded from http://trned.lyellcollection.org/ at Yale University on July 9, 2015

4 EDINBURGH GEOLOGICAL SOCIETY. value. It occurs in patches in the fields, along slightly raised ground, extending from Lochend to East Row House, a distance of fully a mile. Mr Gibson, the farmer at Lochend, informed us that " marl," which we afterwards found to be diatomite, was turned up in ploughing operations in the fields following a line close to the Leven, and extending from his farm eastward to Auchmuir Bridge, a distance of fully two miles. This " marl" bleaches white, remains lumpy, and is troublesome to break up, thus retarding sowing operations. These patches make bad land and yield poor crops. The soil is thin,.and when trenching we found that a hard plough pan had been formed on the top of the diatomaceous deposit, caused by the plough always penetrating to the same depth. This plough pan will intercept the drainage and in winter the diatomite will become water-logged, creating in spring a cold seed-bed which naturally retards germination. In conversation with Mr Gibson we learned that where the plough had pierced the diatomite and mixed it with the sand below, the soil became greatly improved and much more easily worked. Loch Leven occupies the site of an old glacial hollow; at that time a natural barrier probably extended across the narrow neck at the east end of the present level carse, through which the river Leven flows. Here at present the intrusive sheets forming the high ground and known locally as Kinneston Craigs on the north and Bell Crags on the south practically meet. As the ice receded, the hollow would be dammed back at this point. The melting ice left accumulations of sand and gravel on the floor of the basin. Shallow eskers were formed, upon which the diatomaceous earth was subsequently deposited. It may be noted that all streams draining into Loch Leven flow from a northerly or westerly direction. Sediments carried along with them will naturally fall to the bottom of the Loch long before their waters approach the outlet at the east end. In that area the deposits will invariably be organic in origin. Here the diatomaceous earth and lake peat were laid down. Denudation would gradually break down the dam at the east end and lower considerably the volume of water, laying bare a large extent of level ground. In 1845 a large reclamation scheme was completed. The present " New Cut" was then opened. This is practically a level cutting extending from Auchmuir Bridge to the sluices at the east end of the present loch, a distance of nearly three miles. By this means the waters of the Loch were lowered 4| feet, and nearly one-fourth of its area dried up. In the Annual Report of the Scottish Fishery Board, 1898, Downloaded from http://trned.lyellcollection.org/ at Yale University on July 9, 2015

A DEPOSIT OF DIATOMACEOUS EARTH, KINROSS-SHIRE. 5

Mr T. Scott, dealing with the pelagic and other organisms found in Loch Leven, says, " Infusoria and micro-algae, which were moderately frequent on three previdus occasions, were quite abundant in the Loch in June, but these minute forms did not appear to be generally diffused, apparently occurring in shoals, and being particularly plentiful to the south of Reed Bower," thereby indicating that diatomite may be in course of formation at the present day. Deposits of diatomaceous earth have been recorded from various Scottish localities, viz., Aberdeenshire, Skye, Mull and Lewis. That from Black Moss, Dinnet, Aberdeenshire, was described in 1882-3 in vol. iv. page 207 and pages 277-282 of the Transactions of this Society. It has been worked extensively since then and the work is still going on. The Skye deposits are described in vol. v. page 318 of this Society's Transactions. They have been worked almost continuously since then up to last summer, when work ceased, and since then very little has been done. Notice of the Mull deposits is found in the Quarterly Journal, Microscopical Society, vol. i. page 92, and in vol. ii. pages 24 and 90 of the Proceedings of the Royal Society, Edinburgh.