This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1923 edition. Excerpt: ...the solvent action of percolating waters. Newly formed limestone may contain abundant interstices between the calcareous fragments of which it is composed. However, on account of the ease with which the calcareous materials are compacted or are dissolved and again precipitated, the original interstices tend to close up ot-to. become filled Hence, the older limestones are generally compact and impervious except in bedding planes and joints (PL IX, A and B) and in passages developed by solution, generally along bedding planos or joints (PI. VII, B). If the formation has always lain at considerable depths, under conditions of sluggish water circulation, it is likely to be a poor source of water. If it has been in a topographic or structural position that induced active circulation of water it is usually cavernous and is likely to be a good aquifer (PI. X, A). The limestone is dissolved most rapidly above the water table, where there is abundant and rapid percolation and where the percolating waters contain carbon dioxide, which is necessary for dissolving limestone. However, the crevices that occur above the water table are not available as reservoirs of ground water; only those below the water table can yield permanent supplies to wells. Obviously an ideal sequence of events has occurred where a limestone was exposed to leaching until it became cavernous and was then subjected to changes that raised the water table and immersed the cavernous part in the zone of saturation. This sequence of events has occurred in the north-central United States and has made excqtient aquifers out of some of the prominent limestones of that region, such as the Galena limestone and the Niagara limestone. Before the glacial epoch these limestones lay at the...