The most common and most likely answer to this crossword clue is the 9 letter word FORELANDS
I've seen this crossword clue in The Guardian
F
O
R
E
L
A
N
D
S
Buddy explains!

The straight part
We know that "Outstanding features, in the main/Outstanding features, in the main" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case outstanding features, in the main/outstanding features, in the main = forelands.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does FORELANDS mean?
FORELANDS noun- A headland.
- In plate tectonics, the zone adjacent to a mountain chain where material eroded from it is deposited.