### Clue: One called initially to step up to create glacial mass (3,3)
### Answer: ICE CAP 
 ### Explanation: Definition: glacial mass
 I(Roman numeral for "one") + **1st letter of**(… initially) "called" **plus**(to) **reversal of**(… up, in a down clue) PACE(a single step).
Defn: A covering of ice over a large area.