I remember reading a novel about the discovery of an ancient reptilian race discovered in a subterranean cave system. I thought it was written by Robert Silverberg but can't find it in his list of books. I think it was a YA novel. It was probably written in the 50s, 60s or early 70s.

closed as too broad by Adamant, QuestionAuthority, TheLethalCarrot, Valorum, Rand al'Thor Aug 10 at 10:21

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    I believe there are a few books with similar themes, can you remember anything else about this? What happens in it? How are they discovered? Etc. If you can remember anything else please edit in. – TheLethalCarrot Aug 10 at 8:22
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    Because these are based on old Hollow Earth theories, there are piles of them. E.g. any Doctor Who book about the Silurians. – Adamant Aug 10 at 8:51
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    Welcome to Science Fiction & Fantasy! This question matches multiple works and would be greatly improved by going through the checklists here; How to ask a good story-ID question? to identify any unique features that would distinguish it. – Valorum Aug 10 at 9:53