Seven plates from the 1797 second edition of Jean Claude Delamétherie's 5-volume Theorie de la Terre. I've been mulling over these images for some time, but my lack of French combined with the Internet's lack of much information in English about the man or his work has left me with more questions than answers.

Perhaps the most obvious conjecture is that these diagrams illustrate notions on the structure of the Earth's crust, well before scientists developed the current theory of plate tectonics, which only achieved widespread acceptance in the 1960s.

For French speakers, a very limited Wikipedia article on the man can be found here. I'll update when I have more info.

Files are rather large, 2.5-7mb each.