38 GDIDE TO LOCALITIES. 



The Cambric and Recent beds are represented best in the im- 

 mediate vicinity of Boston, but occur in many places in eastern 

 Massachusetts. The Neocene, Cretacic and Jurassic (?) are con- 

 fined to the South Shore islands, while the Eocene is found only 

 as transported material in the drift plains of Truro, Cape Cod. 

 The Triassic is confined to the Connecticut valley. The Car- 

 bonic is found in many places in eastern Massachusetts, but its 

 fossils are few. The Devonic has so far been identified definitely 

 in only one locality on the Connecticut river, — i. e. Bernardston, 

 Franklin county. 



CAMBRIC SERIES. 

 A. Lower Cambrian beds. 



1. EAST POINT, NAHANT. 



Boute. — From Lynn (see pp. 10-11) by barge or bicycle across Nahant 

 Neck to the Lodge estate ; follow footpath to cliff on the left ; barge fare, 

 $.25 round trip. 



The stratified rocks of East point, Nahant, consist of altered 

 slates and limestones of Eocambrian age, as first definitely ascer- 

 tained by Foerste. The limestone beds furnish fossils which, 

 up to the present time, number only a few species in all. They 

 are chiefly species of Hyolithes, and appear usually as cross or 

 longitudinal sections on the rock surfaces. In the former case 

 they exhibit more or less distorted rings, according to the di- 

 rection of the section ; while in the latter case they are marked 

 by lines, either parallel or converging. The shells differ slightly 

 in color and texture from the enclosing rock, and on this account 

 can be seen on the sections. As a rule, however, it takes some 

 time before one becomes accustomed to recognizing these minute 

 markings. Complete specimens can be obtained only by breaking 

 the rock carefully with a hammer; and considerable time and 

 patience are necessary to insure a fair reward. 



A common species is Hyolithes communis, var. emmvnsi, charac- 

 terized by the semicircular outline of its cross-section, the flat- 

 tened side occasionally becoming concave. H. communis, a more 

 slender form with a nearly circular cross-section, occurs fre- 

 quently. H. princeps, a large species, often with sub-semicircular 

 cross-sections half an inch or more in diameter, is not infrequent; 

 and H. im.par with a regularly oval section also occurs. In addi- 



