I don't collect. I buy piles of stuff and flip what I can, so a $300 book for buttons I might not ever find again is a lot.
Had no idea asking for a picture of a page was a problem but I had an issue on another site where someone told me I had X and I priced accordingly on ebay, it sold FAST, then they messaged me saying they were wrong and it was, in fact, Y. So, I have that experience. And what would a 1900 button be doing in a book for buttons no newer than 1865? (and I got three sources saying the marking is Civil War, one from this forum.
https://civilwartalk.com/threads/general-service-buttons.208161/)
Can I at least get an ID on the button? Probably not US military. Might be novelty for all I know. Scovill probably made for all kinds of markets.