Well done Raul on persevering with the earthcache theme. I prefer earthcaches that deal with economic geology or aspects related to it but an earthcache is an earthcache and will always be welcome.
A while ago on one of my earthcaches a comment in the log stated that the place was perfect but all that was missing was a Tupperware. I strongly disagree with that statement and here is why: If you go to school, or lessons, the only Tupperware that should be visible should contain your lunch, not a tiny notebook, dodgy gifts and least of all wrapped in a black plastic bag that turns into rubbish a few weeks later.
Earthcaches are meant to be educational, i.e. to make the observer aware of an aspect that would have otherwise gone unnoticed. While observing the outcrop of this cache, I noticed that all passers by couldn’t care less about their prehistory. A sign of the times no doubt. What’s important are the mp3, playstation, pda, cell phone, etc. Your cache will make a few more people aware of their prehistory.
The fact that the area was previously covered by the sea is indeed common a common occurrence given the multitude of limestones that abound in the Lisbon area. Limestone is mainly made of calcite and all limestone forms from the precipitation of calcium carbonate from water either with or without the help of living organisms.
You can look simplistically at this formation in two ways:
1- Without the aid of living organisms: If water containing calcium carbonate (eg. sea water) is evaporated, the calcium carbonate will crystallise out of solution.
2- With the aid of living organisms: Many marine organisms extract calcium carbonate from seawater to make shells or bones. Mussels, clams, oysters, and corals do this. So too do microscopic organisms such as foraminifera – important in the petroleum industry. When the organisms die their shells and bones settle to the seafloor and accumulate there. Wave action may break the shells and bones into smaller fragments, forming a carbonate sand or mud. Over millions of years, these sediments of shells, sand, and mud may harden into limestone.
The process involves some chemistry and mass balance as well but that I’ll leave that behind for a later, more technical session.
Thank you Raul for taking me back to Sedimentology 101 and I would like to reinforce a request that I had already made when we were discussing the text of the cache page. The people/visitors to the site will have a clearer picture of the type of organisms that are depicted on outcrop if you place an image of them on the actual page. The tiles on site are informative but look like pictures taken with a rolleiflex in 1931. Thanks for the excellent earthcache.