The geology of Orange County is as varied as its topography. Along the eastern feet of the Shawangunk Mountains are Heidelberg limestones, gray and Medina sandstones, shales and grits, and the mountain rocks are mostly sandstones, shales and grits. The grits extend along the top of the range through the county and are from 60 to 150 feet thick. Heidelberg limestone extends from the Mamakating valley to the Delaware River. Grit and red rocks are on the west side of Greenwood Lake, and grit of various colors extends from Round Hill to Woodcock Mountain, and is also found in the southwest base of the Schunnemunk range and in Pine Hill. Grawacke is the rock on the southeast side of the Bellvale range in Warwick, and is found in the town of Blooming Grove in the Schunnemunk range. The Hudson River group occupies a large part of the surface of the county, and consists of slates, shales, grits, limestones, breccias and conglomerates. It extends from the Hudson River through Warwick to the Jersey line, and from the Hudson at Cornwall Landing to four miles above Newburgh. It is stratified with grawacke and grawacke slate. It forms the surface rock of the most of Goshen and Blooming Grove, and parts of Cornwall, New Windsor, Newburgh, Montgomery, Hamptonburgh, Crawford, Wallkill, Mt. Hope and Minisink. Dark Utica slate is found on the banks of the Hudson near Newburgh. Trenton limestone appears in Hamptonburgh near Mount Lookout, and this mountain is composed of Black River limestone, which is also found on Big Island in the Drowned Lands and in Minisink. There is a bed of blue limestone about a mile wide extending from the Hudson at Hampton southeasterly through Newburgh into New Windsor. It is also found in the towns of Cornwall, Blooming Grove, Warwick, Monroe and Goshen. Oolitic limestone is on Big Island, near New Milford, and on Pochunck Neck. Slate rocks of the Taconic system are above Newburgh, and its limestone between the Highlands and Grove Pond Mountain. Its white limestone appears in Warwick, where it is in narrow ridges separated by other rocks. It is also found along the shore of the Drowned Lands at Amity, and near Fort Montgomery in the Highlands, from which it may be traced by way of Little Pond across the Ramapo. In some localities it is so white as to be translucent. Many different minerals are found in it.