

\begin{longtable}{|r|r|r|r|}\hline
   \multicolumn{4}{|c|}{Extreme Observations}\\\hline
   \multicolumn{2}{|c|}{Lowest} &    \multicolumn{2}{|c|}{Highest}\\\hline
   Value &    Obs &    Value &    Obs\\\hline
\endhead
   3.8 &    50 &    4.5 &    48\\\hline
   3.8 &    47 &    5.0 &    41\\\hline
   3.8 &    45 &    5.3 &    49\\\hline
   4.1 &    44 &    5.8 &    42\\\hline
   4.5 &    48 &    6.6 &    43\\\hline
\end{longtable}

