Réserve naturelle nationale d'Hettange-Grande, National nature reserve in Hettange-Grande, France

The Réserve naturelle nationale d'Hettange-Grande covers 6 hectares around the former Gries quarry in Moselle. Its low, pale grey and tan rock face, rough and layered with moss and soil, is the Hettangian stratotype: 25 m of massive Hettange sandstone, with gryphaea limestone and lumachelle beds. Grasses and shrubs line the top edge, with two slender trees at the right end.

In 1864 the Swiss geologist Eugène Renevier proposed the former Gries quarry as the international reference section, or stratotype, for a new geological stage, the Hettangian, spanning 199.6 to 196.5 million years ago. The quarry had been worked since Roman times for paving stones, rubble and sand until the mid-20th century, and the site became a national nature reserve by decree on 4 April 1985.

The name Gries comes from the quarry whose sandstone was worked since Roman times for paving stones, rubble and sand, until extraction stopped in the mid-20th century. The reserve keeps the quarry name, and visitors can still read the cut rock faces of the old workings.

The reserve lies in the former Gries quarry and its adjoining land in Hettange-Grande, in the Pays des Trois Frontières near the German and Luxembourg borders. The site is managed by the Communauté de Communes de Cattenom et Environs, which took over in 2013. Look for the fossils, the different rock types, a discontinuity surface and a fault that make the site a teaching ground for Earth sciences.

The former Gries quarry exposes a 25-metre-thick bed of Hettange sandstone, a massive quartz-rich rock formed from sands laid down offshore. Beds of lumachelle, a hard rock of cemented shells and pebbles washed in by storms, are intercalated in it. Visitors can also spot a fault and a surface of discontinuity among the exposed rocks.