Measure of course is microscopic. On the contrary, it's earth-shaking! (7)
I believe the answer is:
seismic
'earth-shaking' is the definition.
(I've seen this in another clue)
'measure of course is microscopic on the contrary' is the wordplay.
'SEISMIC' is hidden in amongst the letters.
However, I'm not sure how the hidden word is indicated.
'it's' is the link.
Can you help me to learn more?
(Other definitions for seismic that I've seen before include "Of earth tremors" , "earth-shattering effects?" , "like tremors?" , "of enormous proportions" , "Resulting from earthquakes" .)