In Chapter 10 we get something in the way of a physical description of Elinor & Marianne -- not a lot, but more than JA sometimes gives us.

Miss Dashwood had a delicate complexion, regular features, and a remarkably pretty figure. Marianne was still handsomer. Her form, though not so correct as her sister's, in having the advantage of height, was more striking; and her face was so lovely, that when, in the common cant of praise, she was called a beautiful girl, truth was less violently outraged than usually happens. Her skin was very brown, but from its transparency, her complexion was uncommonly brilliant; her features were all good; her smile was sweet and attractive; and in her eyes, which were very dark, there was a life, a spirit, an eagerness which could hardly be seen without delight.

Elinor was very pretty, but Marianne was strikingly beautiful. If the narrator had stopped there, we could have imagined the details for ourselves. Now we have a little more to go on: Elinor's delicate complexion vs. brown but transparent skin w/ a brilliant complexion. I read it that Marianne is taller, but I think it can also be read the opposite (and I'm not sure that it matters, except for how I see the two sisters in my mind).