I have a problem in understanding of a sentence
The old woman, lying back so quietly among her pillows with closed eyes, yet with that look of singular intentness and concentration, was seeking no lover of her youth; though, indeed, she had had one once, and from time to time he did enter her revery, try as
She would to prevent him. At that point, she always made the singular comment, "Gone past! I must be getting back to the beginning," and, pressing back into her earliest consciousness, she would remount the flooding current of the years. Each time, she hoped to get further, —
Though remoter shapes were illusive, and, if approached too closely, vanished, — for, once embarked on her river of memories, the descent was relentlessly swift. How tantalizing that swiftness! However she yearned to linger, she was rushed along till, all too soon, she sailed into the common light of day. At that point, she always put about, and laboriously recommenced the ascent.
I cant understand the bold part