Compaction and diagenesis (the complex processes of transformation of sediment into rock) often efface most obvious traces of limestone's formation, but sometimes exceptional preservation reveals features familiar from the present world.
The Caverna de las Brujas (Cave of the Witches) near Malargue, south of Mendoza in Argentina is a cave complex in a fossilised Jurassic-Cretaceous limestone reef sequence at the foot of the Andes. The name comes from an oral tradition that Mapuche shamans used to gather there for ceremonies or that 2 white captives escaped there and flew out of it. Other legends recount intense lights shining from the cave, supposedly during magical rituals.
The image is of a fossilised cave (about 3x2 metres) within the reef which has been preserved nearly intact . Those of us who snorkel or scuba dive can nearly see the light shimmering in the water, crinoids on the walls and strange fishes swimming around inside.
Such a clear and detailed glimpse of a long gone world makes it real in a way that textbooks never can. It also demonstrates that while reef building organisms might change in the periodic mass extinction events that punctuate Earth history, the structures that result can remain remarkably similar from era to era. Seeing such examples induces an awe inspiring feeling of intimate contact with deep time that is hard to cultivate in any other way, and which us poetically inclined geoscientists thrive on. It also demonstrates that in life's evolution, plus ca change, plus c'est la meme chose (otherwise known as convergent evolution, but that's another story).
The image was taken by the author during a visit to the cave.
Here is a basic primer on limestone formation:
These links are in Spanish, but can be pasted into google translate for a rough rendition.