Thirtieth Annual Reunion of Fiftieth and Fifteenth New York Engineers. The Engineers' Brigade, Army of the rotouiac, held its thirtieth annual reunion in Geneva yesterday. There were about 2X) survivors of the brigade in attendance. The brigade was composed of the Fiftieth ana Fifteenth New York Volunteer Engineers, Engineers, which were recruited in Central and Southern New York. The Fiftieth was raised ia 1m11, and participated in almost almost every battle and skirmish in which the Army of the Totomac took part. The soldiers of the brigade were builders, not fighters. They lail out camps, planned and built fortifications, built roads and laid and took up pontoon bridges. The regiments in the brigade were broken up into detachments of one and two companies companies each, and were never all together except when they were mustered into the service of the national government. The most important work of the brigade was done on the fortifications around Petersburg, Fredericksburg, Spottsylvania, Wilderness, Cold Harbor, Gettysburg and Richmond. The public exercises of tbe reunion were held in the opera house at 2.i0 o'clock yesterday afternoon, followed by the business meeting behind closed cloor3.