geology: north shore. 11 



By wheel, over Charlestown bridge, through City square, Charlestown ; 

 over elevated bridge to Chelsea, through Broadway, Chelsea, to Lynn. 

 From Lynn, by barge, wheel, electric, or afoot, to Lynn beach, walking 

 thence southeast to Eastern point on Great Nahant, malting observations 

 en route. Return to Lynn may be all the way by barge if desired, for 

 most of the trains; barge fare, single, $.15, round trip, $.25. 



Lynn beach, from Lynn to Little Nahant, offers an excellent 

 opportunity for tlie study of marine constructive action. The 

 bouldery character of Marblehead Neck is absent except at the 

 ends. The variations in texture along its course and upward from 

 tide-line to crest can be seen plainly. The remnants of a few 

 dunes stand by the roadside. Ripple-marks, wave-marks, rill- 

 marks, trails, impressions of organic forms, etc., are abundant 

 at low tide. Rafting in of pebbles and shells attached to Lami- 

 naria is a common sight, especially after easterly storms. The 

 spit-building has progressed from both ends ; but there is such a 

 preponderance of southward motion, that, as can be seen in the 

 field, the union of the two spits was close to Little Nahant. The 

 beach is very recent, and growing rapidly. (See also Zoology, p. 

 77 ; Botany, p. 97.) 



Little Nahant consists of syenite, and a small amount of sed- 

 imentary rock on its northwest side ; the latter quartzite and meta- 

 morphosed green slates, with a strike N. 50° E., and a dip 70° 

 S. E. The whole is intruded by trap dikes of diabase or basalt, 

 probably of the same late series as those at Clifton and in Somer- 

 ville. The glaciation offers little of interest. In what appear to 

 be sheltered spots on the northwest slope, some eolian action is in 

 progress. Marine effects are shown here and at Great Nahant as 

 well as anywhere on the coast, especially with reference to lines of 

 weakness. The cliffs of Little Nahant give indication on the north 

 side of a twenty-five foot marine bench, possibly postglacial. The 

 appearance is clearer on the east end of the land. Numerous 

 dike chasms, especially on the south side, give effective exhibitions 

 of the wearing action of the waves at high tide, by their ceaseless 

 pounding and reflow. Joint chasms present the same appearance ; 

 and in one instance — "Irene's grotto," on the southeast side of the 

 peninsula — a large section of rock has disappeared below, leav- 

 ing a solid roof above. The place hardly can be dignified by the 

 name of cave, but is only an arch ten or fifteen feet long. Pro- 



