_Crystallized Calcareous Spar._--This mineral occurs, in minute rhomboidal crystals, in the calcareous rock of the Island of Michilimackinac. Sometimes these crystals fill cavities or seams of the rock, or are studded over the angular surfaces of masses of vesicular limestone of that island. I also found this mineral at Dubuque's mines, and in small crystals in the metalliferous limestone bordering the Fox River, between the post of Green Bay and Winnebago Lake, where it is associated with iron pyrites and blende. Subs. 2.--_Compact Limestone._ In proceeding northwest of Detroit, this mineral is first observed, in situ, on an island in Lake Huron. It is afterwards found to be the prevailing rock along the south and southwest shores of Lake Huron. In many places, it incloses fossil remains. Sometimes it is _earthy_, as at Bay De Noquet, a part of Green Bay, on Lake Michigan, where it contains very perfect remains of the terrebratula. (Parkinson.) In other places, no remains whatever are visible, and the structure is firm and compact; or even passes, by a further graduation, into transition-granular, of which, it is believed, the west shores of Lake Michigan afford an instance. It is most commonly based upon sandstone, which also contains, in many places, the fossil organized remains of various species of crustaceous animals, and of vegetables, sometimes, coal, &c. Subs. 3.--_Agaric Mineral._ This mineral substance occurs in crevices and cavities in the calcareous rock of the Island of Michilimackinac, Michigan. Subs. 4.--_Concrete Carbonate of Lime._ 1. _Calcareous Sinter._--In the form of _stalactites_ and _stalagmites_, in a cave situated near Prairie du Chien, on the Upper Mississippi. 2. _Calcareous Tufa._--A remarkable formation of tufa is seen on the east banks of the Wabash River, near Wynemac's Village, about ten miles above the junction of the Tippecanoe. It extends for several miles, and is deposited to the thickness of thirty or forty feet above the water, forming cliffs which are covered with alluvial soil and sustain a growth of forest trees. The precise points of its commencement and disappearance were not observed. The structure is cellular or vesicular, and resembles, in some places, a coarse dried mortar. It is very light, and possesses a white color in inferior situations, but the surface is somewhat colored by fallen leaves and other decaying vegetation. It imbeds fluvatile shells and some vegetable remains, the species of which have not been ascertained. The opposite, or west side of the river consists of a kind of puddingstone, or caschalo, made up of pebbles of quartz, &c., cemented by carbonate of lime, of a yellow color and translucent. This beautiful aggregate is overlayed by a stratum, of fifteen or twenty feet in thickness, of diluvial soil. These localities fall within the limits of the State of Indiana; but on territories still occupied, if not owned, by the aborigines.