Greece was covered by a shallow, oxygen rich sea during most of the Triassic, Jurassic, Cretaceous and even later. A continuous submerging allowed the formation of huge layers of limestone in the whole area. But then, during the Cretaceous, a big island appeared, which run from north to south, in the area between Thesaloniki and Athens. Here the layers were partly eroded, and today we find here many crystalline rocks and also most valuable resources of Greece, like coal, manganese or iron ore.
Whith the alpine orogeny, the formation of the Alps, the limestone was lifted all over the country and folded. So today about two thirds of the area of Greece is covered with limestone. Caves are very common, as many other karst phenomena.
The whole mediterranean area is an active, converging plate rim, where the African and the European Plate collide. Still, most of the action happens in Italy, with ongoing volcanism. In Greece, there is little volcanism, but sometimes heavy earthquakes and now and then some thermal springs.