This was the verse

Exodus 10:21 

And the Lord said unto Moses, 

Stretch out thine hand toward heaven, 

that there may be darkness over the land of Egypt, 

even darkness which may be felt.

That Mathew Henry was referring to in his commentary on 

Joel 2:2

A day of darkness and of gloominess, 

a day of clouds and of thick darkness, as the morning spread upon the mountains:

"...even darkness which may be felt."

Tell me were not there.

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Exodus 10:22-23

And Moses stretched forth his hand toward heaven; and there was a thick darkness in all the land of Egypt three days:

They saw not one another, neither rose any from his place for three days: but all the children of Israel had light in their dwellings.

I love you honey.