From the northern side of 96th St. the outside tracks rise and after crossing over the inside tracks they are brought together on a location under the center line of the street and proceed along under the boulevard to a point between 122d and 123d Streets. At this point the tracks commence to emerge from the tunnel, and are carried on a viaduct along and over the boulevard at a point between 134th and 135th Streets, where they again pass into the tunnel under and along the boulevard and Eleventh Ave. to a point about 1350 ft. north of the center line of 190th St. There the tracks again emerge from the tunnel, and are carried on a viaduct across and over private property to Elwood St., and over and along Elwood St. to Kingsbridge St. to Kingsbridge Ave., private property, the Harlem Ship Canal and Spuyten Duyvil Creek, private property, Riverdale Ave., and Broadway to a terminus near Van Cortland Park. That portion of the line from 96th St. to the above-mentioned terminus at Van Cortland Park is known as the West Side Line. The total length of the rapid transit road, including the parts above and below the surface ground of the streets, as well as both the East and West Side Lines, is about 22¹⁄₂ miles. _Material Penetrated._--The soil through which the road was excavated was a varied one. The lower portion of the road, or the part including the loop up to nearly Fourth St., was excavated through loose soil, but from Fourth St. to the ends it was excavated in rock. The loose soil forming the southern part of Manhattan Island is chiefly composed of clay, sand, and old rubbish--a soil very easy to excavate. Water was met at some points, but not in such quantities as to be a serious inconvenience. From Fourth St. to the ends of both the east and west side lines, the soil was chiefly composed of rock of gneissoid and mica-schistose character, these rocks prevailing nearly throughout the whole of Manhattan Island. The rock, as a rule, was not compact, but full of seams and fissures, and at many points it was found disintegrated and alternated with strata of loose soils, and even pockets of quicksand were met with along the line of the road. _Cross-Sections._--The section of the underground road is of three different types,--the rectangular, the barrel-vault, and the circular. The rectangular section. Fig. 119, is used for the greater part of the road, of which a portion is for four tracks and a portion for two tracks. The dimensions adopted for the four tracks are 50 × 13 ft., and for the double tracks 25 × 13 ft. The barrel-vault section, composed of a polycentric arch, having the flattest curve at the crown, has been adopted for the tunnels under Park Avenue--while the semicircular arch is used for all the other portions of the road to be tunneled. The circular section of 15-ft. diameter is used under the Harlem River, and being for single track, two parallel tunnels were built side by side.