Complex sentence: In a letter to Maurice Adams, BH Cunningham described the graves, 5 to 7 in number, "radiating from a common centre like the spokes of a wheel", but unfortunately he had made no notes of his finds and was writing from memory.
Split into simpler sentences: In a letter to Maurice Adams, BH Cunningham described the graves, 5 to 7 in number, "radiating from a common centre like the spokes of a wheel". Unfortunately he had made no notes of his finds, and was writing from memory.