mile from northwest to southeast. Although small, this area is economically one of the most important in Maryland.
The granite is entirely surrounded by the Baltimore gneiss, of preCambrian age, into which it is intruded. No dikes or apophyses of the granite have been observed penetrating the surrounding gneiss, but that the gneiss is older than the granite is shown by the large number of inclusions of the gneiss incorporated in the granite. These are described in some detail on pages 46-47.
The systems of horizontal and vertical joints are prominent!y developed in these quarries, especially in the Guilford and Waltersville (Pls. IV, B, and VI, B) and the Weller quarries.
A chemical analysis of the granite from Woodstock is given in column 4 of the table on page 42. A noteworthy item in this analysis is the large percentage of soda, which indicates the presence of much soda-lime feldspar.
The granite bowlders first attracted- attention to this area and operations were begun about 1832-33. The principal demand at first was that by the Baltimore and Ohio Railroad for stone for bridge and culvert work. One of the most important of the early contracts for the granite from Woodstock was that for the Baltimore customhouse about 1873-74.
DESCRIPTIONS OF QUARRIES:
Several extensive quarries have been operated in the Woodstock area. These are the Guilford and Waltersville Granite Company's quarry, the Fox Rock quarry, the Weller quarry, and the Atherton quarry. The first two are the most important and extensive and, together with the Atherton, which had only recently been opened, were operating at the time of the writer's examination in March, 1908. The village of Granite is located within the quarry area. A railroad spur 2 miles long connects the quarry of the Guilford and Waltersville Granite Company with the main line of the Baltimore and Ohio Railroad at Putney & Riddle's bridge, about 1 mile east of Woodstock.
The Guilford and Waltersmlle Granite Company's quarry is the largest quarry in the area. The opening is roughly circular in outline, measuring about 500 by 600 feet, and is worked to an average depth of about 12 feet. (See Pl. IV, B.)
The rock is a biotite granite of medium-gray color and medium grain. Because of slightly increased biotite the granite is a fraction darker in color than the gray granite at Guilford and is of slightly coarser texture." The granite consists of potash feldspar (orthoclase and microcline), soda-lime feldspar (oligoclase), quartz, and biotite, together with accessory zircon, apatite, and allanite and secondary
chlorite, epidote, and muscovite. Orthoclase is partly intergrown with a second feldspar as microperthite. A part of the feldspar shows considerable alteration in some of the thin sections. Intergrowths of feldspar and quartz are abundant. The quartz shows strain shadows and is in places fractured from pressure metamorphism.
The sheets measure from 1£ to 6 feet in thickness and are approximately horizontal (Pl. VI, -B). There are two principal sets of vertical joints, striking about northeast-southwest and northwestsoutheast, and several minor sets having different courses. Many of the joint faces are curved irregularly. They are spaced at sufficiently wide intervals to permit the quarrying of blocks of almost any size. The rock contains some thin pegmatite dikes. A very few dark segregations (knots), of biotite chiefly, the largest rarely exceeding 12 inches in length, were observed.
Physical tests made on specimens of this granite to determine absorption, compressive strength, and freezing loss, the results of which are given on pages 48, 50, show it to be a most durable stone. A chemical analysis is given on page 42 (No. 4).
The product is used chiefly for general building purposes, in both the rough and the dressed states. Other uses are for monuments, paving blocks, some curbing, and crushed stone (mostly for concreting). It is shipped to Maryland, Pennsylvania, New York, Delaware, Washington, D. C., and occasionally to Virginia and Ohio.
The Fox Rock quarry is the oldest one in the area and has been worked to an extreme depth of 96 feet. The rock is a biotite granite of medium-gray color and medium grain. It is entirely similar in color, texture, and composition to that of the Guilford and Waltersville quarry described above. It consists of potash feldspar (orthoclase and microcline), soda-lime feldspar (oligoclase), quartz, biotite, and scant muscovite, together with accessory zircon, apatite, and allanite and secondary chlorite, muscovite, and epidote. The feldspars are partly intergrown in microperthitic structure, and some of them are cloudy and opaque from alteration. Intergrowths of feldspar and quartz are shown.
Vertical joints strike N. 55° E., N. 10° W., and N. 50° W., spaced at intervals of 8 inches to 4 feet and more. There are a few pegmatite dikes of small thickness. Occasional dark segregations (knots), of biotite chiefly, occur in the granite. The thickness of the decay at the surface ranges up to more than 15 feet in places.
The principal uses made of the product are for general building and monumental work and for street curbing and paving blocks. No crushed stone is produced. The product is shipped to Pennsylvania and West Virginia and to various points in Maryland. Occasionally it has been shipped as far west as Indiana and as far north as New York.
The Weller quarry is adjacent to the Guilford and Waltersv'ille quarry on the west. It was the only quarry in the area not operating at the time of examination, in March, 1908. It had apparently been idle for some time, as the opening, which is a large one, probably 300 feet long by 100 feet wide and 70 feet deep, was nearly filled with water, and very little could be seen of the actual quarry conditions. (See Pl. V.)
The rock is a biotite granite of the same color, texture, and composition as that at the Guilford and Waltersville and the Fox Rock quarries, already described. The effects of weathering along vertical and horizontal systems of joints are probably the most characteristic to be found within the State. Keyes ° has described it as follows:
The quarry ledge has the appearance of a great wall of cyclopean masonry, layer upon layer of huge blocks, rising one upon another with the regularity and precision of human workmanship. The separate blocks are more or less obloug in shape, and often measure 15 to 20 feet in length and from 2 to 8 feet in height. They are all more or less rounded, the spaces between the different bowlders being filled with incoherent granitic sand, derived from the decomposed edges and the sides of the blocks. It is quite evident that the granitic mass was originally everywhere jointed, and that atmospheric decay took place much faster on the edges and corners than on the flat sides of the great fragments, thus quickly rounding and forming them into bowlders like those found throughout drift areas. The sandy matrix is usually from 5 to 10 inches in thickness. The interior of the bowlders is perfectly fresh, and affords the best of rock for building purposes. As decomposition progresses the amount of interstratified sand greatly increases, and the blocks become proportionately smaller.
The Atherton quarry is a short distance west of the Guilford and Waltersville quarry. It was opened about eighteen months prior to the writer's examination in March, 1908, in bowlder exposures of the granite.
The rock is a biotite granite and is entirely similar in color, texture, and composition to that of the other quarries in the Woodstock area, already described. It is likewise equally suited for the various uses made of the granite from the Guilford and Waltersville quarry (p. 58).
PORT DEPOSIT AREA.
Probably the Maryland granite which is best known outside of the State is that quarried in Cecil County, near the northern limits of the town of Port Deposit, on the northeast side of Susquehanna River. The value of this granite was early recognized, and it was quarried for foundation stone for the oldest colonial dwellings. Though it was worked in a small way for many years, the quarrying industry may be said to date from the years 1816 and 1817, when stone was quarried for the bridge built across Susquehanna River.
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