What rambler among old lime-quarries is not familiar with the stone-lily, so abundant an organism in most of the Palæozoic and many of the Secondary limestones? In some beds of the carboniferous limestone its abundance is almost incredible. I have seen a weathered cliff in which its remains stood out in bold relief, crowded together, to use an expression of Dr. Buckland's, "as thickly as straws in a corn-rick." The joints of this animal, known now as _entrochi_ or wheel-stones, forced themselves on the notice of men during even the middle ages, and an explanation was soon found for their existence. From their occurring largely about the coast at Holy Island, they were set down as the workmanship of Saint Cuthbert. "On a rock by Lindisfarne, St. Cuthbert sits and toils to frame The sea-born beads which bear his name." The aged saint was represented as employing his nights in this highly intellectual task, sitting on a lone rock out in the sea, and using an adjacent one as his anvil. "Such tales had Whitby's fishers told, And said they might his shape behold, And hear his anvil sound, A deaden'd clang,--a huge dim form Seen but, and heard, when gathering storm And night were closing round." But these wheel-stones were not the only geological curiosities to which this simple mode of explanation was applied. In the same storied neighbourhood there occur in considerable numbers the round whorled shells of the genus _Ammonites_. These were gravely set down as petrified snakes wanting the head, and their petrifaction and decapitation were alike reverently ascribed to the power of the sainted abbess of Whitby. "They told How of a thousand snakes each one Was changed into a coil of stone When holy Hilda prayed." The stone-lily belonged to that large class of animals ranked together as _Echinodermata_, a name taken from one of the leading subdivisions of the group--the _Echini_ or sea-urchins. It seems to have been one of the earliest forms of life upon our planet, its disjointed stalks occurring largely in some of the oldest Silurian limestones. In the Secondary ages it began gradually to wane, until at the present day its numerous genera appear to be represented by but the _comatula_ and the _pentacrinite_, two tiny forms that float their jointed arms in the profounder depths of the sea. [Illustration: Fig. 19.--_a_, Cyathocrinites planus. _b_, Encrinal stem, with uniform joints. _c_, Single joint, or wheelstone.]