Read this: A band of Middle Devonian limestone runs west to east from Cremyll to Plymstock including the Hoe. Local limestone may be seen in numerous buildings, walls and pavements throughout Plymouth. To the north and north east of the city is the granite mass of Dartmoor; the granite was mined and exported via Plymouth. Rocks brought down the Tamar from Dartmoor include ores containing tin, copper, tungsten, lead and other minerals. There is evidence that the middle Devonian limestone belt at the south edge of Plymouth and in Plymstock was quarried at West Hoe, Cattedown and Radford.

What river was used to ferry granite from Dartmoor to Plymouth?
What is the answer? (If it cannot be answered, return "unanswerable")
Tamar