Let’s clear up some confusion: “Delta blues” doesn’t refer to the river delta itself but rather the 200-mile stretch of the Mississippi beginning just south of Memphis. It’s here, famously tagged “The Most Southern Place on Earth,” that Charley Patton, Son House, Robert Johnson and other drifting musicians hammered out a regional take on country blues that is legendary for its slide guitar and harrowing emotions. The bulk of the movement’s most important recordings appeared in the late ’20s and ’30s, while many of its stylistic trademarks would live on in Chicago blues, British blues, and even early hard rock.