Large layers of cross-bedded sand can be indicative of a environment.

Layers of cross-bedded sand can be indicative of a DESERT environment wind is responsible for the formation of these sedimentary structures. Sand dunes preserved in rocks can be quite large. These structures form as a result of the migration of dunes due to the action of the wind. Dunes are not often preserved but a few can be observed in thick sandstone units. 

This is what i found on google“ the monomers combine with each other via covalent bonds to form larger molecules known as polymers. in doing so, monomers release water molecules as byproducts. this type of reaction is known as dehydration synthesis, which means “to put together while losing water. in the process, a water molecule is formed.” i hope this you

The direction a chemical reaction occurs is represented by an arrow