It runs along the shore for several miles, and terminates on the beach near a long reef. Its course from this point is west, a little northerly, along the old frontiers of the province of Chihlí, and then in Shansí, till it strikes the Yellow River, in lat. 39-1/2° and long. 111-1/2°. This is the best built part, and contains the most important gates, where garrisons and trading marts are established. Within the province of Chihlí there are two walls, inclosing a good part of the basin of the Sangkan ho west of Peking; the inner one was built by an emperor of the Ming dynasty. From the point where it strikes the Yellow River, near Pau-teh, it forms the northern boundary of Shensí, till it touches that stream again in lat. 37°, inclosing the country of the Ortous Mongols. Its direction from this point is north-west along the northern frontier of Kansuh to its termination near Kiayü kwan, through which the road passes leading to Hami. From near the eastern extremity of the Wall in the province of Chihlí, extending in a north-easterly direction, there was once a wooden stockade or palisade, forming the boundary between Liautung and Kirin, which has been often taken from its representation on maps as a continuation of the Great Wall. It was erected by the Manchus, but has long since become decayed and disused. The entire length of the Great Wall between its extremities is 22-1/2 degrees of latitude, or 1,255 miles in a straight line; but its turnings and doublings increase it to fully 1,500 miles. It would stretch from Philadelphia to Topeka, or from Portugal to Naples, on nearly the same latitude. The construction of this gigantic work is somewhat adapted to the nature of the country it traverses, and the material was taken or made on the spot where it was used. In the western part of its course, it is in some places merely a mud or gravel wall, and in others earth cased with brick. The eastern part is generally composed of earth and pebbles faced with large bricks, weighing from 40 to 60 lbs. each, supported on a coping of stone. The whole is about 25 feet thick at the base, and 15 feet at the top, and varying from 15 to 30 feet high; the top is protected with bricks, and defended by a slight parapet, the thinness of which has been taken as proof that cannon were unknown at the time it was erected. There are brick towers at different intervals, some of them more than 40 feet high, but not built upon the Wall. These are independent structures, usually about 40 feet square at the base, diminishing to 30 at the top; at particular spots the towers are of two stories.