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The Oeningen strata consist of a series of marls and limestones, many of them thinly laminated, and which appear to have slowly accumulated in a lake probably fed by springs holding carbonate of lime in solution.
But since their deposition these ancient sediments have been crumpled and crushed, broken with great faults, and extensively metamorphosed. The limestones have recrystallized into marbles, among them the famous marbles of Vermont; the Cambrian sandstones have become quartzites, and the Hudson shale has been changed to a schist exposed on Manhattan Island and northward.
The conversion of the limestone and these and many other instances into a siliceous rock, effervescing slowly with acids, would be difficult of explanation, were it not ascertained that such limestones are always impure, containing grains of quartz, mica, or feldspar disseminated through them.
The geological agency which has been potent in giving the remarkable crater-like form to Montezuma Well was correctly recognized by Dr Hoffman and others as the solvent or erosive power of the spring. There is no evidence of volcanic formation in the neighborhood, and the surrounding rocks are limestones and sandstones.
I noticed on the north-west extremity of the basin of the West Indies that the secondary formations dip towards south-east; along the coast of Venezuela rocks of gneiss and primitive mica-slate dip to north-west. The basalts, amygdaloids, and trachytes, which are often surmounted by tertiary limestones, appear only towards the eastern and western banks.
The sandy limestones of the Calciferous record the transition stage from the Cambrian when some sand was still brought in from shore. The highly fossiliferous limestones of the Trenton tell of clear water and abundant life. We need not regard this epicontinental sea as deep.
In other cases interbedded limestones and other sedimentary rocks containing marine fossils prove that at times subsidence has gained on the upbuilding and the delta has been covered with the sea.
For carbonate of lime is a widely-spread substance, and is met with under very various conditions. All sorts of limestones are composed of more or less pure carbonate of lime. The crust which is often deposited by waters which have drained through limestone rocks, in the form of what are called stalagmites and stalactites, is carbonate of lime.
Every building is seen to be a remnant of once continuous beds of sediments, sand and slime on the floor of an ancient sea, and filled with the remains of animals, and every particle of the sandstones and limestones of these wonderful structures to be derived from other landscapes, weathered and rolled and ground in the storms and streams of other ages.
"We can make a lovely corner-piece out of it; there's all those limestones down in the yard, and some of them are such pretty shapes, that will look lovely set in moss, with vines going over them. We can hang the baskets in the windows, and when the curtains are fresh and clean, it will look so pretty." "Hurrah for my better half," cried Kat, with a flourish of her hat.
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