Totally agree that nineteen century readers had much smaller internal libraries of remembered visual images to draw on than we typically do. I suspect that at least some of those readers had developed their abilities to take in authors’ lengthy descriptions and build robust mental pictures from them. It’s easier and maybe a better strategy for us to pull up an image from memory or with Google for “Colorado mining town” or whatever than mentally build one following an author’s description, but really digging into the description and making something out of it can be its own experience.