Some notes on the distribution of erratics over eastern Moray

Abstract

Several well-marked boulder streams may be traced across the area between the Lossie and the Spey. These streams are found to cut one another's paths at various angles, while over a certain portion of the field there is distinct evidence that the ice-streams that conveyed the erratics must have moved from directly opposite points of the compass. The various boulder streams will now be described in detail. A. The most important stream came from the west. It is characterised by a large and varied category of boulders, some of which are traceable to well-known origins, but to a large number of them no definite locality can with certainty be assigned. Conspicuous among them, however, are blocks of the (1) porphyritic granites of Ardclach and Kinsteary. These granites are by no means easy to distinguish by the naked eye. For this reason, microscopic examination of sections from such blocks as were found in unexpected positions has been resorted to as a means of diagnosis. The Ardclach rock is somewhat lighter in colour, and usually shows finely-marked zonings of its porphyritic felspars, a characteristic which is entirely absent in the Kinsteary rock. Microscopically, the former granite shows muscovite in parallel intergrowth with the ordinary black mica in almost every mica cluster; while the Kinsteary only shows this arrangement—and then not very typically—in perhaps a single cluster out of several slides. The inclusions in the quartz grains of the two granites are also markedly different. Blocks of Kinsteary granite have been observed in