Properties of the Garnet Group. 49 



page 443 of the System of Mineralogy with the decidedly 

 higher values given with analyses of almandite and spessartite 

 on the preceding pages of that book. While the relationship 

 between specific gravity and refractive index is often a reason- 

 ably definite one, there are apparently frequent exceptions to 

 the rule which at present do not admit of explanation. It is 

 only by the accumulation of large amounts of data concern- 

 ing these relationships in minerals that we can hope eventually 

 to be able to make a satisfactory statement of the principles 

 involved. 



Mineralogical Laboratory of the Sheffield 

 Scientific School of Yale University, 

 New Haven, Conn., Dec. 1st, 1914. 



Art. IV. — The Lower Ordovician (Tetragraptus Zone) at 

 St. John, New Brunswick, and the New Genus Protisto- 

 graptus ; by F. H. McLearn. 



(Contributions from the Paleontological Laboratory, Peabody Museum, 

 Yale University, New Haven, Connecticut, U. S. A.) 



In the summer of 1913, during the meetings of the Twelfth 

 International Geological Congress, held in Canada, the members 

 of the Al Excursion, under the leadership of Doctor G. A. 

 Young, were permitted to see the intricate geology of the city 

 and environs of St. John, JS'ew Brunswick. Fossils were 

 collected by members of the party from the Cambrian, 

 Ordovician and Carboniferous formations, but as those of the 

 oldest period are well known to geologists through the long 

 labors of Doctor G. F. Matthew, Professor Charles Schuchert 

 devoted more time to the Ordovician which yields the 

 graptolites. Because of the great stratigraphic value of these 

 fossils, another and larger collection was made by Professor 

 Schuchert and the writer in the spring of 1914 at the same 

 place. All of this material has been studied in the Paleonto- 

 logical Laboratory at Yale University, by the writer, under the 

 direction of Professor Schuchert, and the results are presented 

 below. 



The faunas of the St. John Group are familiar to all paleontol- 

 ogists. The life record opens with the provincial Protolenus 

 fauna. The widespread Paradoxides fauna of Middle Cambrian 

 time follows, which at certain horizons is very abundant, 

 although the trilobites are fragmental. Higher occurs the 



Am. Jour. Sci. — Fourth Series, Vol. XL, No. 235. — July, 1915. 

 4 



