moulds of minute fossils which have been removed by solution. The massive rock is largely made up in places of stems of crinoids--stone lilies which grew in the greatest profusion in these quiet waters--and the tilted layers may be made of casts and moulds of unbroken shells of little bivalves. Occasionally the saucer shaped tail and head-shields of a characteristic trilobite are found piled together and unbroken. Coral are very common in this ancient reef rock, a form resembling honeycomb being especially noticeable. And as one floats down stream at the base of the cliffs he can hardly fail to notice large tapering segmented shells, either straight or slightly curved, representatives of the cephalopod mollusks. The picturesque rock walls of the Palisades, which rise perpendicular for as much as ninety feet from the water's edge, are due primarily to the great resistance of the LeClaire rock, due to its chemical composition--for dolomite weathers far less rapidly than a non-magnesian limestone--and to the fewness of those planes of weakness called joint-planes. The joints of the LeClaire are distant and vertical. The stone breaks down, therefore, in immense blocks where undercut by the river which leave for ages the scarp behind them as a vertical wall. Because of its qualities the LeClaire is one of the best lime rocks in the country. The impurities of the clay, the iron and silica which it contains, may run as low as one-third of one per cent. The large per cent of carbonate of magnesia present makes it a cool lime, slow to slack and slow to set, and it is to such limes that architects, masons, and plasterers now invariably give preference over the so-called hot limes burned from non-magnesian limestones. The hardness and durability of mortars made from the LeClaire rock limes approaches that of cement, and after thirty-five or forty years of weathering, joints in mason work seem almost as fresh as when first struck. The extreme hardness of the rock and the slowness with which it weathers make it specially valuable for crushing for macadam and ballast. The _Anamosa phase_ of the Gower limestone is typically exposed in the large quarries at Anamosa and Stone City, Mount Vernon and Waubeek. It is a light buff or yellow limestone, with constant, parallel, and horizontal or gently inclined laminated layers. The limestone is soft to work but hardens on exposure. The saw encounters no obdurate materials and the chisel finds the fracture even and regular. Bedding planes are so even and smooth as to be at once ready for the mortar with little or no dressing. Much of the stone can be split horizontally to any desired thickness, while the distant joints permit the quarrying of blocks beyond the facilities of transportation or any possible use. Many layers are so homogenous that they can be wrought into fine carvings.