On the laws that govern the rounding of particles of sand

In my inquiry into the origin of the sandstones of Eastern Moray I have had frequent occasion to note the various degrees of rounding presented by the various mineral particles that enter into their composition. During the last three years I have examined a large number of specimens from all the sandstone formations represented in the area, and from all important divisions of these formations. Amid much that was variable in the highest degree, it soon became evident that so far as the rounding of the constituent particles was concerned, a certain amount of uniformity prevailed, and though from a very early period of the inquiry it was no less evident that quite a number of factors entered into and co-operated to produce the results observed, it was nevertheless soon recognised that these results were fairly constant, and in the majority of cases strictly comparable from specimen to specimen. In order if possible to discover guiding principles, the better to compare past with present conditions, and generally it might be to illustrate both, I examined the sands of the rivers of the adjoining land area, the sands of the shore of the Moray Firth, and the sands of the sand dunes of Culbin. All these, though often in less degree, appeared to illustrate the operation of the same general principles. It was very early noted that the size of the particles within certain fairly defined limits at either end had a decided bearing on their degree of rounding. Over and