How do geologist know what they are looking at really is what they say it is?

Hi edge...Too busy to really be involved, but I have been lurking Anyway, I was thinking that since the topic is "How do geologists know..." the topics of grain shape (or roundness) and sorting should be covered, since those are major factors that help determine deposition environment.Also you mentioned chemical and mechanical weathering in the context of the production of the sediment; but don't those processes also occur during and after lithification? And don't those characteristics give us clues as to the depositional environment?HBD