induration. 1. the process of hardening or being hardened.
1 They're weak against the Ice and Water types in reference of erosion, which cause this elements to the ground. 2  They're immune against the Electric type because in real life, the ground is a natural sink of electrons.  The Bug type resists them because many bugs like worms live inside the ground and many of them eat it.
The following argument is weak because the statistic is not clearly at one of the two extremes: 1  Many American firefighters are of Irish heritage. 2  My new neighbor is an American and a firefighter.