Porkuni quarry is situated in the Porkuni park forest and is not with natural origin. Limestone was broken here for building the Porkuni Bishop’s Castle in the 15th century. Fortunately the upper layers of Ordovician deposit were exposed here within 5.5 metres. The upper mentioned layers contain lots of fossils, for what reason they have become famous all over the world. Throughout times more than 150 different kinds of fossils have been initially described here, on account of which this outcrop is called the stratotype (the most characteristic cross-section) of Porkuni deposit.
Very few places of finding of fossils of this particular period are known elsewhere.