Lower case letters that come after the capital letter(s), e. g., kjk, labeling a rock unit represent the rock unit's

Represent a rock type or rock unit

Explanation:

The alphabetical symbols are one of the important features that are used in the geological maps. It uses a combination of capital as well as small letter, where the capital letter is used in the front depicting the age of the rocks and one or more small letter is used behind that represents the type of rock or rock units.  

For example, Ks would represent the symbol for a shale rock which formed in the Cretaceous period.

Thus, the lower case letter that comes after the capital letters signifies the rock type (or rock unit).

since there isn't any suggested answers i will give you the reason and hopefully you can figure it

south africa, or rather all of africa, has not been in the location in which it is nowadays throughout the geological past. after the super-continent pangaea started to break apart, gondwanaland, in which was africa, moved further south, and parts of it came to be very close to the south pole. because the climate in this part of the world is very cold due to the very dispersed sun rays in there, what is now south africa, started to freeze, and the conditions were right for the formation of glaciers. the glaciers existed up until the period when gondwanaland started to break apart and what is now africa started to move towards north, sp it warmed up and the glaciers melted.