226 PROCEEDINGS OP THE AMERICAN ACADEMY 



confined exclusively to the slates at different levels, in a height of 

 twenty-seven hundred feet. 



This "Group of St. John," also called "Acadian Group," must be 

 regarded as the up[)er part of the St. Albans Group, for the fossils 

 indicate a lower level than the iauna of the " Georgia slates " with 

 Olenellus ; but they are not far from these ; the Brachiopods resemble 

 them very much, and the Trilobites have affinities with tliem, while 

 they have Sl fades of greater antiquity, because of the Parodoxides and 

 a considerable number of Conocephalites, 



As to the stratigraphy and the fossils, Mr. Matthews says : " No 

 trace of a fos.-^il could be seen in the black slate. But scattered at 

 intervals through some of the bands of this slate were hard, com- 

 pact masses of rock, which, when broken, were found to be packed 

 with fossils. The spherical and elliptical masses, which varied in size 

 from about a yard in diameter to nodules of one inch across, had the 

 appearance of imbedded boulders, but the fossils in them were always 

 parallel to the stratification, and similar fossils were subsequently 

 found in irregular beds and lenticular bands of hard rocks. In the 

 boulder-like masses there were numerous layers loaded with organic 

 remains, which extended without diminution in the number of the fos- 

 sils to the very edge of the block, where they suddenly disappeared, 

 and not a trace of them could be found in the adjoining slate rock." * 



There is a repetition of what I have pointed out on the borders of 

 Lake Champlain and at Point Levis, only the lenticular masses are of 

 smaller dimensions, and recall those of Scandinavia. 



liraintree^ near Boston^ Massachusetts. — Ten miles south from 

 Boston, in direct contact with the syenitic granite of Quincy, are sev- 

 eral quarries of argillites, two of which contain two trilobites rarely 

 to be found ; — one very large, the head or cephalic shield reaching 

 even a foot in width, the Paradoxides Harlani Green ; the other very 

 small, almost minute, Arionellus quadrangularis Whitf. Beside these, 

 a Cephalopod perhaps and a marine plant. These fossils are only 

 found within a space of a few scjuare yards ; much narrower limits 

 than the fauna of St. John, New Brunswick, or any of the localities 

 of the fossiliferous Taconic on the borders of Lake Champlain. 



Braintree evidently belongs to the '• Zone of Paradoxides," in the 

 lower part of this zone, and I place it, until the contrary is proved, 

 below the " Acadian Group " of St. John, and about the middle of 

 the " St. Albans Group." 



* Ilhistrations of the Fauna of tlie St. John Group, p. 90. 



