Relating to a geosyncline; describing large-scale sinking areas of the Earth's crust where thick sediment layers accumulate.
From 'geosyncline' plus '-al' (adjectival suffix), creating an adjective describing features related to geosynclinal basins.
Geosynclinal theory was revolutionary in the 1800s—it explained how mountains form from layers of sediment that sink deep into the Earth and then get crushed and thrust upward by tectonic forces.
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