Progress and problems in the selection of stratotypes for the bases of series in the Ordovician System of the historical type area in the U.K.

Fortey, R. A., Bassett, M. G., Harper, D. A. T., Hughes, R. A., Ingham, J. K., Molyneux, S. G., Owen, A. W., Owens, R. M., Rushton, A.W.A., Sheldon,P. R.