While I was, some time ago, officially inspecting the cotton-factory of Messrs. J. Finlay and Co., at Catrine, in the county of Ayr, on going over the bleaching-establishment attached to it, I was struck with an unusual appearance of a part of the machinery, which, at a distance, looked as if it were made of brass. On a closer examination, I found that it was a large circular wooden box coated with an incrustation of a brown compact substance, having a highly polished surface, a metallic lustre, in some places beautifully iridescent, and when broken exhibiting a foliated texture. This resemblance in structure and pearly lustre to some species of shells, such as the Meleagrina, Maleus, Avicula, Ostrea, Pinna, and others, induced me to examine the substance more closely, conceiving that it might possibly throw some light on the formation of shell. The part of the machinery on which I observed the incrustation is called a Dashwheel, and consists of a circular box, about seven feet in diameter and three feet in width, revolving upon a horizontal axis, and having its interior divided into four compartments, into each of which there is a circular opening on one side. The purpose of this wheel is to wash or rinse the cloth in pure water, after it has been boiled or steeped in the bleaching-liquors. It makes twenty-two revolutions in a minute, which is found to be the proper degree of speed, in order that the cloth may be tossed about and dashed against the sides as the wheel turns; a greater velocity causing it to keep at the circumference without shifting its position.