Learn English – Correct usage of “cover a lot of ground”

I can't think of any expressions that are specific to the case of noticing a recent change, but there are a number of common expressions that can be used whenever someone says something that should have already been obvious. Here are a few:

• "Thank you, Captain Obvious." (Captain Obvious, naturally, commands the Starship Duh.)
• "No duh."
• "No shit." (Or "No shit, Sherlock.")
• "You don't say!"
• "What else is new?"

Note that some of these are more sarcastic than others. In particular, as CarSmack and J.R. point out below, "No shit" and "No shit, Sherlock" are harsher, and I wouldn't use them with casual acquaintances. J.R.'s alternative suggestion, "No kidding", is less harsh.

In this case, "the whole ground" is a metaphor meaning a very wide range. So his "gifts, and instincts, and feelings, and interests" cover a lot of topics. To put it another way, he is interested in a lot of different things, and feels a lot of different things, and so on.

Mark Twain is a delightful author, but he is best known for how he captured the patterns of speech of the poor and uneducated in the late 1800s. I highly recommend his works, but they are probably not the best source if you are trying to learn English. His idioms, sentence structure and often his spelling are archaic now, and were often considered wrong even at that time by educated people.