GEOLOGT : NORTH SHORE. 13 



strata, which dip landward ; hence the irregularity of the projec- 

 tions, the presence of stacks, joint chasms of great length, etc. 

 Dike chasms are abundant. The best is the " Devil's bridge," a 

 little north of Pulpit rock (the best-formed stack) . Here a part 

 of the dike remains and forms a natural bridge. The action of 

 the waves at high tide is worthy of close attention. 



On the north side of Great Nahant, a fair bench has been 

 formed by the sea. Follow the cliff walk southward, crossing 

 a coarse pebble beach to the next rocky headland, to where the 

 north-south road ends. From here, in front of a dwelling house, 

 a path leads down to Swallow's cave, perhaps the finest cave on 

 the coast. It can be explored only at low tide, and will be found 

 to extend through the cliff from end to end, and to terminate up- 

 ward in an arched roof, broken only by one circular window. 

 Near the outer end the tunnel is divided by a projecting piece of 

 the country rock, where the eroded dike itself formerly was 

 divided. The tunnel is long and high and narrow, and on its bot- 

 tom are several tidal basins filled with water. For this portion of 

 the trip, arrangements can be made with the barge driver to call at 

 the cave at any hour, thus saving further walking. The spouting 

 horn, a miniature dike cave, can be visited by leaving the barge 

 on the north shore (the main road to East point) just east of 

 Castle rocks, where a path leads northward to the horn, whose 

 location is marked by a bench on the summit of the cliff. The 

 visit should be made at half-tide, and the view gained from below. 

 Here, as so often on this coast, care is necessary to prevent a rep- 

 etition of the too frequent accidents. A satisfactory trip can be 

 made by asking the barge driver to stop first at the spouting horn 

 at the ebb tide. He will drive to a point west of the horn, whence 

 a path leads eastward. Follow the path east and south beyond 

 the horn, striking the road near Castle rocks. A short walk will 

 bring one to the entrance to the Lodge estate. Walk from here 

 by the foot-path to East point, going later to the cave as already 

 directed. (See also Palaeontology, p. 38; Zoology, pp. 85, 87; 

 Botany, p. 97.) 



Literature. 



Foerste, A. K. — The paleontological horizon 'of the limestone at 

 Nahant, Mass. (Bos. Soc. Nat. Hist., Proa, vol. 24, pp. 261-263) 



Lane, A. C. — The geology of Nahant. (Bos. Soc. Nat. Hist., Proc, 

 vol. 24, pp. 91-95.) 



