Complex sentence: Since his time, archaeological excavations have added enormously to the knowledge of ancient Greece, but scholars still find much of value in his detailed historical and topographical discussions of different sites, and his eyewitness accounts of Greece at the end of the 19th century.
Split into simpler sentences: Since his time, archaeological excavations have added enormously to the knowledge of ancient Greece. There is still much of value in his detailed historical and topographical discussions of different sites and his eyewitness accounts of Greece at the end of the 19th century.