First geological map of Britain, detail of the north east coast (figure 8). This map was published in 1815 by British geologist William Smith (1769-1839). It shows rock layers (strata) in England and Wales and part of Scotland (key at lower left). Smith's work as a canal surveyor allowed him to study geology. He discovered that geological strata could be reliably identified at different places on the basis of the fossils they contained. Smith also proposed the principle of superposition, that if a strata overlays another then it was laid down at a later time. He is considered the father of English geology.