...nitial cannonade was intended to subserve the additional purpose of a signal, by which the Confederates before Mechanicsville might be advertised of his presence. For many hours' the brigades of A. P. Hill had been patiently awaiting the expected sound, before the enemy's works. They now pressed forward, and a furious cannonade opened on both sides. General Hill, supported by Ripley's brigade, of D...