I agree with your analysis of the first sentence, but the second still sounds awful and stilted to me! I'd rewrite as: > >The Upper Paleolithic cave art of Eur

I agree with your analysis of the first sentence, but the second still sounds awful and stilted to me! I'd rewrite as: > >The Upper Paleolithic cave art of Europe was a tradition that lasted for perhaps 20,000 years and it will always be rightly described as primitive. But it is upon those anonymous artists' shoulders — giants' shoulders — that later masters were able to stand. Picasso himself declared: 'After Altamira, all is decadence.' What's the point of "mercurial" or "Spaniard" being included? Irrelevant detail that, frankly, trips my tongue up when reading (and when my tongue trips, I stumble slightly even while silently reading).