what does 'available Megaliths' mean in the descriptions of "The Shifting Stone" and "The Heart of the Earth"?

[Apl4U]

According to the rulebook for English, the description for the two Megaliths is as follows:

The Shifting Stone
Duplicate and apply the effect of one of the available Megaliths.

The Heart of the Earth
Build one of two available Megaliths in one of the empty squares of the play area. This action does not increase your score. (Don’t forget to replace it with a new Megalith.)

In my opinion, looking at the description of 'The heart of the earth,' it seems that 'the two available Megalisths' refers to 'the two upcoming megaliths.' Because it emphasizes not to forget replacing with a new megalith.

However, I'm not sure if "the available Megaliths" in the description of The Shifting Stone refers to the upcoming ones.

Since there are few opponents for game matching, I can't resolve the question through actual gameplay.
Can anyone who has played this game answer?

[tchobello]

Hello,

these are the only available ones...

[Apl4U]

I thought it might be an empty megalith where a shaman could be placed.
of course, now I know what "available" refers in this game