Graphical Correlation The first step towards correlating the three sections was the selection of an initial standard reference section. For this purpose, the Morgan Creek section was chosen because it presented, on average, a higher number of fossil finds for the six species examined. The first and last occurrences of the six species in this section (x-axis) were compared to the first and last occurrences of the same species in the White Creek section (y-axis). The product was Figure 1. Figure 2 is the same graph as Figure 1, but has a line that better fits the data, called a correlation line. The diamond-shaped points are the first occurrences, while the squares are the last occurrences. Early occurrences that are to the right of the correlation line indicate that this species occurs in older rocks in the White Creek section than in the Morgan Creek section. An example of this is the fossil of the species Kingstonia pontotocensis (diamond #4). To temporally correlate this fossil to the Morgan Creek section, the point is plotted horizontally to the correlation line from which the appropriate x value was found (point in the Morgan Creek section). In other words, the first occurrence of this fossil occurred at a related time 133 m from the base of the Morgan Creek section, but due to poor preservation conditions, erosion, or other geologic phenomena, the fossil was actually found 138 m from the base of the Morgan Creek reach. When a final occurrence is to the left of the correlation line, this means that the fossil is found in younger rocks in the White Creek section than in the Morgan Creek section. Kingstonia pontotocensis is another example. To correlate this to the appropriate elevation in the Morgan Creek section, the data point is moved horizontally on the correlation line and from a vertical line to the x-axis it can be seen that the point needs to be adjusted from 145 m to 153 m in the Morgan Creek section. Section of the stream. Using this correlation method, a theoretical section is created by combining the first and last occurrences of both sections. It is important to note that this section is not found in nature; it is simply an idea representing what a section would look like if fossil preservation problems did not exist and all six fossil chains were accurately represented in the rock record.