| rock | (great natural mass of) stone or stone-like material; any special sort of solid material present in great amounts in the earth |
| shell | hard outer cover of certain sea and land animals |
| deposit | solid material put down, specially by water, on some other body; depositing-the process of putting down material in this way |
solution
| substance, specially a liquid, having another substance (solid, liquid, or gas) so mixed with it that .there is a regular distribution of the molecules of the one among those of the other, and the mixed substance gives no sign of the separate existence of the two; the condition of being so mixed in a liquid and so on |
| age | time for which anything has been in existence, how old it is; great stretch of time, division of history |
generation
| the act or process of producing offspring; the group of offspring produced by a given plant, animal, or group; one stage or level in a family-tree |
| environment | place and other outside conditions in which a living thing has its existence and development |
mean
| condition, quality and so on equally far from two opposites, coming between them, specially as taken to be representative of what is most normal, generally come across |
Ogden's Basic English