My son asked me at the beach how are "sand stones" formed. These are the solid (but fragile) sand conglomerates which you can hold in your hand and which crumble to sand once pressed.
I tried some hand waving about "cement-like" formations and how these grains of sands are held together because they dried "in a specific way" but he was not impressed and neither was I.
Is there a name for these structures so that I can look up how they are formed?