Some years before the Second World War I was privileged to carry out some investigations at Buzenol in the south-east of Belgium with regard to the formation of limestone on the ”crons” and the mollusc fauna of this region. Together with Prof. Dr. P. VAN OYE I discovered the presence of the desmidiid Oocardium stratum Naeg., which, together with mosses and some green algae, is the cause of peculiar limestone formations, locally known as ”crons”. For further details concerning these formations I refer to the original publications (HUBERT, 1937; VAN OYE, 1937; VAN OYE & HUBERT, 1937). About three years ago I revisited this area, among other things to visit the open-air museum of Montauban. Among the excavators of the hill-top were Prof. Dr. MERTENS and other Belgian scientists. I availed myself of the opportunity to see the Montauban cron. I found an increase of the vegetation, as mentioned by Prof. VAN OYE in his publication. This increase will be the death to the cron since the quantity of light under the rapidly growing trees and bushes has been reduced. If these trees should be cut down cron formation will increase.