Figure 42.—Type profile, provinces of the Mid-Atlantic Ridge
Figure 43.—Tracing of PDR record, Rift Valley, Rift Mountains, High Fractured Plateau, and Upper Step
Figure 44.—Tracing of PDR record, Western Rift Mountains
Twenty-six crossings of the Rift Valley are shown in Figure 45. The profiles can be divided into three groups: (1) single well-developed rift valley; (2) several well-developed deep valleys; (3) no particularly deep central valley. Most of the profiles (20) fall into the first class; the second class is represented by 5, and only 1 falls in the third class.
The topography of the floor of the rift is rough. In no instance has a flat floor been observed. Where the valley is widest mountains a few hundred fathoms high protrude from its floor.