But the crust of the earth varies from almost complete impermeability to almost complete permeability.
Thus despite the impermeability of its mass large springs are occasionally found to issue from the Lower Chalk.
In Cheshire the surface-water trickling through the overlying strata dissolves the salt, which is subsequently pumped as brine, but at Middlesbrough the great depth and impermeability of the strata precludes this, so another method has been resorted to.
By these means practical impermeability was obtained.
A series of experiments and arguments proves to every man that he, as an object of observation, is subject to certain laws, and man submits to them and never resists the laws of gravity or impermeability once he has become acquainted with them.