\begin{figure}[H]
\centering
\begin{subfigure}[t]{1\textwidth}
\includegraphics[width=\textwidth]{Chapters/Pictures/c_4/842/t x p, ts.png}
\caption{Ring 842: Rock. Observations are highly variable for both parameters.}
\end{subfigure}
\hspace{\fill}
\begin{subfigure}[t]{1\textwidth}
\includegraphics[width=\textwidth]{Chapters/Pictures/c_4/598/t x p, ts.png}
\caption{Ring 598: Rock-like mixed. The red circle indicates a sample region where parameters follow the same patterns.}
\end{subfigure}
\caption{Time series plots relating Penetration and Torque Screw for rock.}
\end{figure}
\begin{figure}[H]
\centering
\begin{subfigure}[t]{1\textwidth}
\includegraphics[width=\textwidth]{Chapters/Pictures/c_4/557/t x p, ts.png}
\caption{Ring 557: Soil. Parameters can be seen to overlap as indicated by Arrow 1 and throughout the ring. Arrow 2 shows a region where there is significant changes between parameters before overlapping again.}
\end{subfigure}
\hspace{\fill}
\begin{subfigure}[t]{1\textwidth}
\includegraphics[width=\textwidth]{Chapters/Pictures/c_4/613/t x p, ts.png}
\caption{Ring 613: Soil-like mixed. Throughout the ring, the parameters are strongly correlated and follow an overlapping distribution.}
\end{subfigure}
\caption{Time series plots relating Penetration and Torque Screw for soil.}
\end{figure}