184 Reports & Proceedings — Edinburgh Geological Society. 



During the wlaole period when the strand-lines were forming in 

 succession, Loch Tulla was dammed by a glacier reaching down to 

 Glen Orchy from the Auch Gleann behind Beinn Dorain. At an 

 early stage Loch Tulla was also confined by a glacier blocking the 

 alternative pass which leads by way of Loch Dochard into Glen 

 Kinglass ; and it was under those circumstances that its waters 

 rose until they could escape northwards into the hollow of Loch Ba 

 by cols which became available, one after another, at heights of 

 1,041, 1,030, and 1,020 feet respectively. Later, the pass to Glen 

 Kinglass was barred and the waters of the Loch sank to 816 feet. 

 Nowadays with Glen Orchy freed of ice, the surface level of Loch 

 Tulla only reaches 542 feet. 



3. " Note on the Occurrence of Norwegian Boulders near Ellon , 

 Aberdeenshire." By Dr. Campbell and Dr. Gibb. 



Dr. Campbell exhibited a boulder of typical Rhomb-Porphyry 

 which he found in situ in a thin deposit of boulder-clay, three-eighths 

 of a mile north-west of Arnage House, and four and a half miles north- 

 north-west of Ellon. Dr. Gibb showed two specimens of typical 

 Laurvikite — one collected by himself was found built in the walls 

 of an old house 2 miles north of Ellon, the other was found many 

 years ago in the Ellon district by the late Professor James Nicol. 

 Two earlier records of the occurrence of boulders of Rhomb-Porphyry 

 in Scotland may be recalled : (a) from a recent beach near Portsoy 

 (Mr. H. H. Read, 1919) ; and (6) from a coarse boulder bed under- 

 lying the Lower Grey Boulder Clay at Bay of Nigg, Aberdeen 

 (Dr. Bremner, 1920). 



Evidence is not yet available to demonstrate whether or not the 

 boulders in the Ellon district were transported directly by the 

 Scandinavian Ice Sheet, but some significance perhaps may be 

 attached to the fact that from the same district the late T. F. 

 Jamieson described an " Indigo Boulder Clay " underlying the 

 Lower Grey Boulder Clay. 



21s^ December, 1921. 



1. " The Source of the Purple Zircons in the Sedimentary Rocks 

 of Scotland." By William Mackie, M.A., M.D., D.Ph. 



In a former communication Dr. Mackie drew attention to the 

 occurrence of purple Zircons in many of the sedimentary rocks of 

 Scotland. These Zircons range in colour from faint purplish to 

 a purple so intense as to render the crystal nearly opaque. As a 

 rule they are distinctly rounded, varying from almost spherical 

 through long regular ovoids to shorter, sometimes asymmetrical 

 ovoids. The chief object of the present paper was to trace the 

 source of these Zircons. Dr. Mackie has found that they are of 

 frequent occurrence in the Moine Schists, in the Aberdeen Schists, 

 in the Torridonian, and in all the younger sediments examined. . 



