In the low area of continental slope, radiolaria fossils are poor in the volcanic cinders and turbidite.
陆坡下部区的火山碎屑及浊流沉积物中放射虫化石亦不丰富。
But one of the problems with concrete is that even after it's hardened, it still absorbs water. So the Romans added a mix of volcanic cinders and clay called 「Potsularna」.