The Mohawk Trail (State Highway 2) heads west from the center of Greenfield and crosses the Green River (0.6) before climbing out of the valley. A lookout (2.1) affords an excellent view of the north end of the Connecticut Lowland, and the observation tower on Shelburne Summit (3.2), situated on a shelf cut out of black Ordovician slate (see pp. 35 -37), provides a broader sweep of central New England scenery. Beyond, the upland is gently rolling, trenched by one deep valley at Shelburne Center (6.8). The descent into this valley (5.6) offers a glimpse to the south across the Deerfield River gorge, but the road soon rises again, hovering 300 feet above the sharply incised stream. The Sweetheart Teahouse (9.9) makes use of one of the ideal sites overlooking the gorge and river. The highway to Colrain (10.2) continues straight ahead, but the Trail turns left across the Deerfield River (10.6) and then right in Shelburne Falls. The road left leads to Conway and South Deerfield. Thick, almost horizontal bands of gray granite gneiss are exposed in the road cuts (11.6) along the south bank of the Deerfield River, but the entrenched stream has left so little room for the highway that the latter soon crosses to the relatively low and more hospitable north bank (11.9). For many miles the road follows the stream so closely that spring floods occasionally cover its surface with ice cakes. The drive along this stretch to the next bridge (21.0) contains the most restful scenery on the trip, though the flat open valley is hemmed in by abrupt slopes which rise for 800 feet. Nor does the flatness of the valley harmonize with the mountain-structure of the platy Goshen schist, which stands on edge all along the roadside. Davis Brook (18.7) crosses the route, and the road beside it leads up to the Davis Mine, which once did a thriving business extracting iron pyrites for the manufacture of sulphuric acid. Once more the highway crosses the Deerfield River (21.0) and enters Mohawk Park, which invites the motorist to linger. A mile farther on (22.0) the road leaves the Deerfield River (22.0) and follows the narrow gorge of Cold River, which seems scarcely wide enough to accommodate it. A shady picnic ground and auto camp (23.6) lie just below the narrowest and deepest part of the gorge (24.5), where the crowding summits seem to tower high above the puny cars. The road crosses to the north bank of Cold River (25.8) and climbs a shelf cut into green volcanic schists (25.8 to 27.6). Leaving the gorge (26.6), it ascends to the upland (29.0), while in view below is the laborious route of the Boston and Maine Railroad along the Deerfield and thence through the east portal of the Hoosac Tunnel near Zoar.