Visit Osbornedale State Park for a hike or fishing expedition, then relax with a picnic or visit the nearby Osborne Homestead Museum.

Osbornedale State Park is a great place for any geology enthusiast. Not only are there several different rock types exposed in the park, but also within the park's boundaries there are geologic folds, quarries, and abandoned mines. Additionally, families can enjoy the wonderful Kellogg Environmental Center that is on the park's property

As you enter the park on the red trail, you first encounter a large outcrop of schist, a metamorphic rock that has undergone intense heat, pressure, and the actions of hot fluids. By definition, schist contains more than 50% platy and elongate minerals such as mica and amphibole. This high percentage of platy minerals allows schist to be easily split into thin flakes or slabs. Part of the Carrington Pond Member, this schist outcrop is an inter-layered gray, rusty weathering schist. The schist outcrop contains several quartz crystals, parallel fractures, and folds. Folds are formed by tensional stress that permanently bends and deforms the rock, as opposed to breaking or fracturing the rock (Figure 1). This can only occur when the rock is deeply buried, where it experiences great heat and high pressure.

As you continue down the red trail, you will encounter a quarry. The area quarried is part of the Harrison Gneiss, a dark gray gneiss that contains biotite, quartz, and feldspar. Similar to the Carrington Pond Schist, the Harrison Gneiss shows extensive folding as well (Figure 2). Gneiss (pronounced "nice") is a high grade metamorphic rock subjected to intense heat and pressure during formation. Gneiss is easily identifiable by the segregation of light and dark minerals giving it a banded texture.

Gneiss usually consists of mostly elongated and granular, as opposed to platy, minerals. The quarry was active at one time and still shows evidence of rocks being removed from the site (Figure 3).

Further down the red trail, there is an abrupt change in the geology. The rocks along the trail change from gneiss to basalt and then back to gneiss. This transition of rock types is due to a dike, which is a sheetlike body of igneous rock that cuts across layering or contacts in the rock into which it intrudes. The dikes located in Osbornedale State Park are all feeder dikes, which help supply the large lava flows in the Hartford Basin 200 million years ago. This particular dike is composed of diabase, a fine-grained igneous rock that cooled rapidly near the earth's surface. In Figure 4a, there is a clear contact between the basalt, which is very dark, and the gneiss, which is gray. In some areas along the trail, the basalt dike is nearly 100 feet wide. After you cross the dike and the stonewall along the trail, you will reach another outcrop of gneiss, indicating you have left the basalt dike area. Following the trail down the hill, you will encounter a large pegmatite outcrop. Pegmatite is an igneous rock that formed from molten rock buried deep below the surface of the Earth. Since the molten rock was well insulated beneath the surface of the Earth, it cooled very slowly, allowing the crystals to grow very large. Pegmatite generally has grains larger than 1 cm in diameter, by definition. This pegmatite contains feldspar, quartz, and biotite. Pegmatite intrusions are of great interest to mineral collectors because they may contain a variety of rare minerals. However, this pegmatite outcrop does not contain any rare minerals (Figure 5).

Osbornedale State Park is located in the Naugatuck Valley Hills just east of the Housatonic River in Derby and Ansonia. The land was once the lushly forested hunting grounds of the Paugussett Indians. Fur traders, such as John Wakeman in 1642, were the first people of European descent to move into the Indians' territory. Permanent settlers began arriving in the late 1650's. The land was gradually purchased from the Paugussetts for items such as clothing or cooking utensils. Because the Europeans concept of property rights was not embodied in the Indian culture, the Indians often sold the same parcel of land several times.

The new settlers cleared the land for farming and took advantage of their location on the Housatonic and Naugatuck Rivers by developing the area into a trading port, which at one time rivalled New Haven harbor. The name of the settlement, originally called "Paugussett" was changed to "Derby" in 1675 after Derbyshire, England, the former home of many colonists.

Though never commercially successful, lands now within the park off Silver Hill Road were mined for silver for a short period after the Revolutionary War. In addition, a spring water bottling business was part of the present park land. In 1956, Osbornedale State Park was willed to the people of Connecticut by Frances Osborne Kellogg, granddaughter of John W. Osborne, one of the Naugatuck Valley's early industrial entrepreneurs.

The prominent Osborne family owned numerous metal working and fabric product factories in the area. At the young age of 24, Frances Osborne, later Mrs. Waldo Kellogg, took over the family business when her father died in 1907. Miss Osborne's decision to take over the family business instead of selling it was contrary to the advice of the executers of her father's estate, and a brave undertaking for a woman in the early part of the century. Despite the prejudices against woman in business at that time, Mrs. Frances Osborne Kellogg was very successful in her many businesses and investments. By adhering to the belief that one should always buy land but never sell it, Mrs. Kellogg gradually acquired the numerous separate farms which now comprise the 350 acre Osbornedale State Park, an unusually large property in the Derby-Ansonia area.

Two very successful farms known as the Osbornedale Farms, were owned and operated by Mr. and Mrs. Kellogg. One farm was a breeding farm for the prize winning Osbornedale Holstien cows. The other farm, acquired from the Basset family, was an excellent milk-producing dairy farm of Jersey cows. Both farms claimed champions in their fields.

Connecticut has made state parks, forests, trails, historic sites and beaches more accessible to our residents so they can enjoy the many attractions and beauty they offer. Under the Passport to the Parks program, parking fees are now eliminated at Connecticut State Parks for those with Connecticut registered vehicles. You can view the CONNECTICUT PASSPORT TO THE PARKS web page to learn more.