Нет. Очевидно. he was star­ing be­fore him with a smile so fixed and pebble-beached

Тогда не знаю. В словарях только одно значение для pebble beach - галечный пляж: https://www.collinsdictionary.com/dictionary/english/pebble-beach

Идиома. Спасибо в любом случае!

I read the passage in the book and it makes absolutely no sense to me. I've never heard it in my life, and, looking online, there's no other instance of it except in this book. But the rest of the words are also strange and the grammar is really weird, so maybe that book isn't the best learning resource. This isn't an idiom... it's an attempt to describe someone's smile as a lineup of pebbles along the shore of his mouth. Definitely passive vocabulary! If you ever tried to use this in the modern English, nobody would know what you were talking about.

Thanks, Uly!

You’re welcome 😉

Uly, dies it mean something like кривая улыбка?

I think it’s more about his teeth, they look like a row of pebbles on a beach

Улыбка обнажила ряд неровных, словно галька на пляже, зубов ?

Вот именно! Молодца)

Thank you, 😁