How does James Herriot use imagery in All Creatures Great and Small?

Example of Imagery:

"The formless heights were resolved into high, grassy hills and wide valleys. In the valley bottoms, rivers twisted among the trees and solid grey-stone farmhouses lay among islands of cultivated land which pushed bright green promontories up the hillsides into the dark tide of heather which lapped from the summits."

Herriot makes great use of detailed, positive imagery to paint a picture of the landscapes he so admires.