=Advantages and Disadvantages.=--Like the Belgian method of tunneling, the German method has its advantages and disadvantages. Since the excavation consists at first of a narrow annular gallery only, the equilibrium of the earth is not greatly disturbed, and the strutting does not need to be so heavy as in methods where the opening is much larger. The undisturbed center core also furnishes an excellent support for the strutting, and for the centers upon which the roof arches are built. Another important advantage of the method is that the construction of the masonry lining is begun logically at the bottom, and progresses upward, and a more homogeneous and stable construction is possible. The great disadvantage of the method is the small space in which the hauling has to be done. The spoil cars practically fill the narrow drifts in passing to and from the front, and interfere greatly with the work of the carpenters and masons. Another objection to the method is that the invert is the very last portion of the lining to be built. This may not be a serious objection in reasonably compact and stable materials, but in very loose soils there is always the danger of the side walls being squeezed together before the invert masonry is in position to hold them apart. Altogether the difficulties are of a character which tend to increase the expense of the method, and this is the reason why to-day it is seldom used even in the country where it was first developed, and for some time extensively employed. For repairing accidents, such as the caving in of completed tunnels, the German method of tunneling is frequently used, because of the ease with which the timbering is accomplished. In such cases the cost of the method used cuts a small figure, so long as it is safe and expeditious. BALTIMORE BELT LINE TUNNEL. In the last few years a modification of the German method was used in this country for the construction of several railroad tunnels. The modification consists in excavating the two-side drifts up to the springing line of the arch of the proposed tunnel. Then a central heading, which is afterward enlarged to the whole section of the tunnel, is excavated close to the crown. At the same time the masonry is constructed from the foundation up in the side drifts. From the floor of the upper section already excavated and strutted, the top of the masonry of the drifts is reached by means of small side cuts; thus the lining is made continuous up to the keystone. The central nucleus or bench is removed after the tunnel has been lined. The most important tunnel excavated by this method was the Baltimore Belt Line tunnel described as follows: