_Feldspar_.--This mineral occurs very plentfully in the space between the limestones and gneiss. It is generally of a flesh red color and often in very perfect crystals, in some instances an inch and a half in length; as its hardness is 6, it can be readily distinguished from calcite, which it much resembles, but which has only a hardness of 3, and dissolves with effervescence in acids. A visit to this locality is a delightful manner in which to spend a holiday or other time of leisure; and as it affords so many interesting and valuable minerals, it forms a very profitable trip as well. In reaching it many interesting localities are passed, and if one has an early start these may all be visited. I will describe a few of these, which are alike possessors of beautiful scenery and instructing geological features and not far from the main line of travel. Starting from the Erie depot, on the Greenwood Lake road, the first stop may be at Arlington, about seven miles west of Jersey City. Here a visit to the Schuyler copper mine may be profitably taken; and as I have written a full account of this locality in a previous portion of these articles,[1] I will not reiterate it here, but refer to that paper. The mine, I might add, is only a mile north of the railroad station, and on Schuyler Avenue, a short distance north from its junction with the Jersey City and Paterson turnpike. Coming back to Arlington depot, and walking on the track for about a quarter of a mile west through the deep cut, the manner in which the sandstones and shales which constitute so large a portion of New Jersey are laid and arranged can be seen to great advantage, this being one of the finest exposures in the formation. At a point about equidistant from either end is a fault in the layers of shales and sandstone; this fault is noticeable as a slight irregularity in the otherwise continuous sides of the cut, and is a point at which the layers of rock on the east have fallen vertically, the western side remaining in its original position. This fault has a thrust of only three feet, but is an instructive example of faults which occur on a tremendous scale in some of the other formations. It will be noticed that between the two edges of the separated layers there is a deposit of a talcky substance, which has been derived from infiltrating waters. Fissure veins are generally in positions of this kind, formed and filled in a similar manner, but with the various metallic ores. Passing further west a short distance we reach the Passaic River, and walk along its banks for a mile north to the Belleville bridge; at this point is the intake of the Jersey City water works, with their huge Worthington pumps and other accessories, which may be conveniently visited. The Passaic River is then crossed, and the train on the Newark and Paterson road may be taken for three miles to Avondale, from whence it is two miles east to the Belleville sandstone quarries, or the bank of the Passaic may be