The name for such a hole is "caldera" which is a word of Spanish origin meaning "a pot" or a "cooking pot" (thing of cauldron!) - and this word is used because it resembles the shape of this hole.
Often the Calderas are filled with water forming lakes and often there is an island in the middle of the water.
Fossils (from the Latin fossilis, which means 'excavated') are the remains or signs of the activity of past organisms.These remains, preserved in sedimentary rocks, may have undergone changes in their composition (by diagenesis) or deformations (by dynamic metamorphism) more or less intense.
