He also found that certain animals were in only certain layers and that they were in the same layers all across England.
While digging the Somerset Coal Canal in southwest England, he found that fossils were always in the same order in the rock layers.
As he continued his job as a , he found the same patterns across England.
Finding the key bed in these situations may help determine whether the fault is a ) are found in a formation, then the inclusions must be older than the formation that contains them.
For example, in sedimentary rocks, it is common for gravel from an older formation to be ripped up and included in a newer layer.
From top to bottom: Rounded tan domes of the Navajo Sandstone, layered red Kayenta Formation, cliff-forming, vertically jointed, red Wingate Sandstone, slope-forming, purplish Chinle Formation, layered, lighter-red Moenkopi Formation, and white, layered Cutler Formation sandstone.
Photo from Glen Canyon National Recreation Area, Utah.Though relative dating can only determine the sequential order in which a series of events occurred, not when they occurred, it remains a useful technique.Relative dating by biostratigraphy is the preferred method in paleontology and is, in some respects, more accurate.Similarly, igneous intrusions cannot cut across or disturb rock layers unless the rock layer was deposited before the intrusion occurred.Unconformities occurs over a long time period when sediment deposition has ceased, erosion removes the top rock layers, and then sediment deposition resumes.Prior to the discovery of radiometric dating which provided a means of absolute dating in the early 20th century, archaeologists and geologists used this technique to determine ages of materials.