The red bus lanes of London

摘要

In his review of the new account of the geology of Northumberland National Park in northeastern England, my friend and fellow Northumbrian, Malcolm Hart, tells us of his experience of road surfaces of red Cheviot felsite when he was learning to drive in the 1960s, and the idea (apocryphal) that red roads 'took priority over black'. This brought back to me my own associations with this distinctive road surfacing, and what it means to Northumbrian geology. First, the stone is an igneous rock for sure, a fine-grained brick-red intrusive on the flank of the main Cheviot granite and the associated red and purple lavas of Devonian age. Without clear contacts, we leave it as 'intrusive'. As for its status in any of the neat classifications of igneous rocks, it seems best to leave it under that vague but comprehensive term 'felsite', coined by Kirwan in 1794 for compact, cryptocrystalline porphyries rich in feldspars. That's how it was taught to me by Professor Serge Tomkeieff when I was a student at King's College Newcastle in 1947, and it remains appropriate for this stone with its uncertain field relationships.