Page:Popular Science Monthly Volume 27.djvu/547

Rh These are all fine-grained stones with but little cementing material, the individual grains of which they are composed being held together simply by the cohesion induced by the pressure to which they were subjected at the time of their consolidation. They therefore work very readily, especially when newly quarried, and have been used more extensively for carved work than any other of our sandstones. They are best represented in the market to-day by the so-called Euclid "blue-stones" and Berea "grits" of Ohio, the former being deep blue-gray in color, while the latter is very light. They are well known to the general public in the form of window stools and caps, door posts and steps, for which purpose they have been very extensively used in all our large cities.

Somewhat resembling in general appearance the Euclid blue-stones, but of greater geological age, are the dark, blue-gray compact "gray-wackes," or flag-stones, so extensively quarried in Ulster County, New York, and other parts of this State and Pennsylvania. These stones are of fine and even texture, and split readily from the quarries in slabs, usually but a few inches thick. They are therefore eminently suited for flagging, to which usage they are extensively applied, though they also used for steps and general trimming purposes. The rock quarried at Barryvale, in Sullivan County, is of a similar nature. It was from quarries at this last-named locality that was taken the monster flag-stone, twenty-five feet two inches long, by fifteen feet wide and eight inches thick, that now forms a portion of the sidewalk in front of the Vanderbilt residence on Fifth Avenue, New York. It should be stated, however, that the size of this block was limited only by the means of transportation, and much larger could be obtained at the quarries if desired.

Another very important group of sandstone, but of still greater geological antiquity, belonging to the Medina period of the Upper Silurian formations, is quarried extensively at Albion and Medina, near Rochester, New York. These stones are usually of a reddish color and contain a larger portion of siliceous cementing material than any of those yet mentioned; they are therefore much harder and much less pervious to moisture. The stones are used for all manner of building purposes, flagging, and street-paving. A somewhat similar stone, but of brighter color and Potsdam age, is quarried in the town of Potsdam, in St. Lawrence County, in the same State. This is the stone used in the construction of the Columbia College buildings in New York city.

Sandstones of this nature, i. e., with the larger proportion of siliceous cementing material, are among the most durable of all our building-stones; but their extreme hardness, and often poor colors are great drawbacks to their extensive use. In process of dressing such stone an exceedingly fine white dust arises and remains for a long time suspended in the air, to the great inconvenience of the workmen, who tell