GLEN ALLEN, Va. (AP) _ Markel Corp. (MKL) on Tuesday reported a first-quarter loss of $52.8 million, after reporting a profit in the same period a year earlier. On a per-share basis, the Glen Allen, Virginia-based company said it had a loss of $6.58. Earnings, adjusted for one-time gains and costs, came to $11.33 per share. The results missed Wall Street expectations. The average estimate of three analysts surveyed by Zacks Investment Research was for earnings of $16.79 per share. The insurer posted revenue of $2.