Coquina in the context of Dunham classification

The Volga Delta is the largest river delta in Europe and occurs where Europe's largest river system, the Volga River, drains into the Caspian Sea in Russia's Astrakhan Oblast, north-east of the republic of Kalmykia. The delta is located in the Caspian Depression—the far eastern part of the delta lies in Kazakhstan. The delta drains into the Caspian approximately 60 km (37 mi) downstream from the city of Astrakhan.

The Volga delta has grown significantly in the 20th century because of changes in the level of the Caspian Sea. In 1880, the delta had an area of 3,222 km (1,244 sq mi). Today the Volga Delta covers an area of 27,224 km (10,511 sq mi) and is approximately 160 km (100 mi) across. It has a classical "delta pattern". The delta lies in the arid climate zone, characterized by very little rainfall. The region receives less than one inch of rainfall in January and July in normal years. Strong winds often sweep across the delta and form linear dunes. Along the front of the delta, one will find muddy sand shoals, mudflats, and coquina banks.

The Castillo de San Marcos (Spanish for “St. Mark’s Castle”) is the oldest masonry fort in the continental United States; it is located on the western shore of Matanzas Bay in St. Augustine, Florida.

It was designed by the Spanish engineer Ignacio Daza, with construction beginning in 1672, 107 years after the city's founding by Spanish Admiral and conquistador Pedro Menéndez de Avilés, when Florida was part of the Spanish Empire. The fort's construction was ordered by Governor Francisco de la Guerra y de la Vega after a raid by the English privateer Robert Searles in 1668 that destroyed much of St. Augustine and damaged the existing wooden fort. Work proceeded under the administration of Guerra's successor, Manuel de Cendoya in 1671, and the first coquina stones were laid in 1672. The construction of the core of the current fortress was completed in 1695, although it would undergo many alterations and renovations over the centuries.