Abundance of the chemical elements of the volatile elements hydrogen, helium, neon, and nitrogen, as well as carbon which has been lost as volatile hydrocarbons. The remaining elemental composition is roughly typical of the "rocky" inner planets, which formed in the thermal zone where solar heat drove volatile compounds into space. The Earth retains oxygen as the second-largest component of its mass (and largest atomic-fraction), mainly from this element being retained in silicate minerals which have a very high melting point and low vapor pressure. The mass-abundance of the nine most abundant elements in the Earth's crust is approximately: oxygen 46%, silicon 28%, aluminum 8.2%,
Lowest bridging point often was at a location that allowed seagoing traffic to approach it from a downstream direction. Examples of lowest bridging points in Britain include London, the lowest bridging point on the Thames; Lancaster, the lowest bridging point on the Lune; York, the lowest bridging point on the Ouse; and Gloucester, the lowest bridging point on the Severn. Glasgow grew up at the lowest bridging point on the Clyde which was about twelve miles upstream from its lowest fording point at Dumbuck. Mathew Paris’s map of 1247 appears to show only one bridge in the whole of Britain: at Stirling, the