Irving uses personification to establish a sense of connection with the mountains, writing that "they will gather a hood of gray vapors about their summits," as if they are human beings putting on clothing.
He also uses juxtaposition, the literary device of placing two ideas or images near each other to establish a comparison or contrast. He does this when he writes:
A termagant wife may, therefore, in some respects, be considered a tolerable blessing.
A termagant wife is one who scolds and bullies; in suggesting this as a blessing, Irving has put two opposing idea together. In doing so, he creates an aphorism, a short, witty statement that contains a truth. Irving's statement is a fresher way of saying every cloud has a silver lining, which means that no matter how bad circumstances are, you can always find some good in them. He also uses alliteration, with the "t" in "termagant" and "tolerable" highlighting those two important words.
Early on, Irving describes the Catskills ("Kaatskill[s]," as he spells them) as "fairy mountains." This foreshadows their important function later in the story as a magical place where Rip will fall under a spell that puts him to sleep for twenty years.