Page 6: wait, I'm confused by the premise here. In panel 4, he says that they found gold on the island and became prosperous. This logically means they were selling the gold so that it was no longer on the island. Then he says the gold ran out, meaning there was no more gold to be found. Then in the next panel, he says the amount of gold "taken from the island" - meaning the gold that was dug up and sold away - was 200kg. So where, in the next panel, does Kindaichi get the idea that the 200kg of gold that was mined and sold away is actually buried on the island?!
And as a side note, why does Kindaichi say "huh? is there such an island?" in that fourth panel? In the first panel he recognizes the island by name and correctly says where it's located, so what the heck is he talking about with that line?