at Pirro Nord, Italy. The mountains of Italy are rising at a rapid rate in the framework of geologic time; at 1.6 mya they were lower and covered with grassland (as much of the highlands still are). Europe was otherwise mountainous and covered over with dense forest, a formidable terrain for warm-weather savanna dwellers. Similarly there is no evidence that the Mediterranean was passable at Gibraltar or anywhere else to H. erectus or earlier hominans. They might have reached Italy and Spain along the coasts. In northern Europe pebble tools are found earliest at Happisburgh, United Kingdom, from 0.8 mya. The last traces are from Kent's Cavern, dated 0.5 mya. By that time H. erectus is regarded as having been extinct; however, a more modern version apparently had evolved, Homo heidelbergensis, who must have inherited the tools. He also explains the last of the Acheulean in Germany at 0.4 mya. In the late 19th and early 20th centuries archaeologists worked on the assumptions that a succession of Hominans and cultures prevailed, that one replaced another. Today the presence of multiple hominans living contemporaneously near each other for long periods is accepted as proved true; moreover, by the time the previously assumed "earliest" culture arrived in northern Europe, the rest of Africa and Eurasia had progressed to the Middle and Upper Palaeolithic, so that across the earth all three were for a time contemporaneous. In any given region there was a progression from Oldowan to Acheulean, Lower to Upper, no doubt. Acheulean in Africa The end of Oldowan in Africa was brought on by the appearance of Acheulean, or Mode 2, stone tools. The earliest known instances are in the 1.7–1.6 mya layer at Kokiselei, West Turkana, Kenya. At Sterkfontein, South Africa, they are in Member 5 West, 1.7–1.4 mya. The 1.7 is a fairly certain, fairly standard date. Mode 2 is often found in association with H. erectus. It makes sense that the most advanced tools should have been innovated by the most advanced Hominan; consequently, they are typically given credit for the innovation. A Mode 2 tool is a biface consisting of two concave surfaces intersecting to form a cutting edge all the way around, except in the case of tools intended to feature a point. More work and planning go into the manufacture of a Mode 2 tool. The manufacturer hits a slab off a larger rock to