In the early 1860s, the discoveries of Boucher des Perthes in France were attracting the attention of British scientists. Boucher des Perthes had found paleoliths in the gravels of the Somme River valley. These implements were older and somewhat cruder than the neoliths Harrison was collecting. Having learned of the finds of Boucher des Perthes, Harrison himself began to search for similar specimens. These Paleolithic implements, although cruder than Neolithic implements, are still easily recognized as objects of human manufacture. They are thus distinct from Eolithic implements. Modern authorities would assign European Paleolithic tools to the Middle and Late Pleistocene. Harrison looked for paleoliths in ancient deposits of gravel on river terraces, and in 1863 discovered his first paleolith in a gravel pit near Ightham (E. Harrison 1928, p. 46). In addition to searching himself, Harrison trained local workmen to recognize flint implements and collect them for him. Over the years, he amassed a substantial collection of paleoliths.
In 1878, William Davies, a geologist of the British Museum, saw some of Harrison’s flint implements and agreed that some of them were paleoliths. Harrison sent a report and some specimens to Sir John Lubbock, who also stated that some of the implements were definitely Paleolithic. G. Worthington Smith, of the Royal Anthropological Institute, visited Ightham and after inspecting the flints initially agreed that some were paleoliths but then later changed his mind (E. Harrison 1928, p. 81).
In 1879, Harrison first met Sir John Prestwich, an eminent geologist, who had a country house eight miles away, at Shoreham. Harrison asked Prestwich some questions about the geological position of the discoveries of Boucher des Perthes in relation to the present level of the Somme River. From Prestwich’s window, they could see the Darent River valley. Prestwich said: “If we take the Darent to be the Somme, the gravels would lie at about the level of the railway station.” The author of Benjamin Harrison’s biography, Sir Edward R. Harrison, wrote (1928, p. 84): “As this remark was made, it flashed through Harrison’s mind that some of his own palaeoliths had been found in gravels that were higher, in relation to the level of the streams to which they belonged, than was the level of the railway station in respect to the Darent. Broadly speaking, greater relative height meant greater antiquity, and, consequently, amongst his finds were implements that might be older than those found by Boucher des Perthes in the Somme valley.”
To further clarify the matter, let us suppose we have a river running on a level plain a million years ago. As it excavates a channel, it will deposit gravel on the terraces of its banks. As the river descends through the strata, it will deposit more gravels at successively lower levels. In this way, it may be seen that the oldest river gravels, about one million years old, would be found at the higher levels of the valley, while the most recent ones would be found at the lowest levels, on the banks of the present river. The ages of the different levels of gravel are therefore the reverse of the ages of a typical sequence of geological strata, in which the higher strata are the youngest and the lower strata are the oldest. It should, however, be kept in mind, that in actual practice, the assignment of ages to river terraces and gravels is rarely so simple as in this hypothetical illustration.
On September 11, 1880, Harrison made a typical discovery. Sir Edward R. Harrison (1928, p. 87) informs us: “He walked to examine a bed of gravel lying on High Field, at the head of the gorge of the Shode. In this gravel, far above the present level of the stream, he found a palaeolithic implement. His thoughts, on making this discovery, must have been somewhat as follows. The gravel was a very ancient gravel, even in a geological sense, and in it was an implement that had been made by man and carried down afterwards by a stream running at a much higher level than the present stream, to the position in which it was found. So man was older than the very old gravel. Harrison sent news of his find to Prestwich, who came at once to Ightham to see for himself the geological position in which the implement had been found.” Prestwich pronounced it a very old bed and advised further research. Prestwich himself and workers under his direction made similar finds.
As word of the newly discovered stone implements spread, James Geikie, one of England’s leading geologists, wrote about them on May 2, 1881 to G. Worthington Smith: “They will yet be found in such deposits and at such elevations as will cause the hairs of cautious archaeologists to rise on end. I hope other observers will take a hint from you and search for paleolithic implements in places which have hitherto been looked upon as barren of such relics” (E. Harrison 1928, p. 91).