38 



TRANSACTIONS OF THE 



both in breadth and length our fragment measures nearly 

 three inches. 



I am indebted to the kindness of Dr. Charles T. 

 Jackson, of Boston, Mass. for this interesting species ; 

 it occurs in magnetic iron ore, and was found by Dr. 

 Jackson and Mr. F. Alger, during their geological tour 

 through Nova Scotia. Their highly important memoir 

 describing the mineralogy and geology of that part of 

 North America, has been justly proposed as a model, 

 both in its generalizations and its details, to future ex- 

 plorers of those districts of our country which yet re- 

 main unexamined and undescribed. According to this 

 memoir, Nova Scotia is based upon granite, although 

 that rock is almost every where covered by more re- 

 cent formations. A transition slate, with marine or- 

 ganic remains; and containing beds of limestone and 

 rich deposits of iron ore, is very abundant. The iron 

 ore is often beautifully impressed with organized bodies, 

 of which our A. crypturus is a fine example. Some- 

 times one portion of a fossil is found moulded in the 

 slate, and the other portion in the iron ore, thus indi- 

 cating their contemporaneous formation. Sandstone is 

 next in extent after the slate, and it is said corresponds 

 geologically, with the new red sandstone or red marl 

 of England. Dr. Jackson, in his letter which accom- 

 panied our fossil, remarks, " \ send you a Trilobite from 

 the mines of magnetic iron in Nova Scotia, which ex- 

 ist in the clay slate of Clements on the Moose river at 

 Anapolis Basin; also a Terebratula found in the same 

 locality. I beg you to show these specimens to the 



