three meters of rock and ash/rock and ash of three meters deep

[diamondcutter]

The volcano was erupting. The ash and rock rose 20 kilometers into the air and spread out like a mushroom across the sky. ...
By midnight three meters of rock and ash had fallen on Pompeii. The danger, however, was not over yet.

(Reading Tracks 3, International Language Teaching Services Ltd)

The “three meters of rock and ash” looks weird to me. I wonder if it’s correct and if I could rewrite it as “rock and ash of three meters deep”.

 

[GoesStation]

The original is not weird. You can't say "of three meters deep". You could say "to a depth of three meters", but the original is better because it's more concise.

 

[tedmc]

It is understood that the three metres refers to the deptth of deposited materials.