Our Volunteers occupying the line of defence north of London, through Epping and Brentwood to Tilbury, had for the past three weeks been in daily expectation of an attempt on the part of the invaders to land in Essex, and were amazed at witnessing this sudden bombardment. From their positions on the northern heights they could distinctly see how disastrous was the enemy's fire, and although they had been informed by telegraph of the reverses we had sustained at Guildford and Leatherhead, yet they had no idea that the actual attack on the metropolis would be made so swiftly. However, they lost not a moment. It was evident that the enemy had no intention of effecting a landing in Essex; therefore, with commendable promptitude, they decided to move across the Thames immediately, to reinforce their comrades in Surrey. Leaving the 2nd and 4th West Riding Artillery, under Col. Hoffmann and Col. N. Creswick, V.D., at Tilbury, and the Lincolnshire, Essex, and Worcestershire Volunteer Artillery, under Col. G. M. Hutton, V.D., Col. S. L. Howard, V.D., and Col. W. Ottley, the greater part of the Norfolk, Staffordshire, Tay, Aberdeen, Manchester, and Northern Counties Field Brigades moved south with all possible speed. From Brentwood, the 1st, 2nd, 3rd, and 4th Volunteer Battalions of the Norfolk Regiment, under Col. A. C. Dawson, Col. E. H. H. Combe, Col. H. E. Hyde, V.D., and Col. C. W. J. Unthank, V.D.; the 1st and 2nd North Staffordshire, under Col. W. H. Dutton, V.D., and Col. F. D. Mort, V.D.; and the 1st, 2nd, and 3rd South Staffordshire, under Col. J. B. Cochrane, V.D., Col. T. T. Fisher, V.D., and Col. E. Nayler, V.D.; the 2nd, 4th, 5th, and 6th Royal Highlanders, under Col. W. A. Gordon, V.D., Col. Sir R. D. Moncreiffe, Col. Sir R. Menzies, V.D., and Col. Erskine; the 7th Argyll and Sutherland Highlanders, under Col. J. Porteous, V.D.; the 3rd, 4th, and 5th Gordon Highlanders, under Col. A. D. Fordyce, Col. G. Jackson, V.D., and Col. J. Johnston--were, as early as 2 A.M., on their way to London. At this critical hour the Engineer and Railway Volunteer Staff Corps rendered invaluable services. Under the direction of Col. William Birt, trains held in readiness by the Great Eastern Railway brought the brigades rapidly to Liverpool Street, whence they marched by a circuitous route beyond the zone of fire by way of Marylebone, Paddington, Kensington Gardens, Walham Green, and across Wandsworth Bridge, thence to Upper Tooting, where they fell in with a large force of our Regular infantry and cavalry, who were on their way to outflank the enemy.