4G4 



THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



Upper." He concludcB by suggesting the inquiry " whether the Eozoon 

 limestones of Canada, which are associated with Laurentian rocks, and 

 Lave been referred to that age, are really Laxxrcntian." 



Professor Hall's idea of making a separate geological formation or 

 system out of tlic limestone masses of Northern JVew York, on account 

 of their unconformable position, is hardly less remarkable than that (jf 

 Professor Emmons, who considered that the peculiar occurrence of this 

 rock in the region in CLuestion could not be accounted for except on the 

 supposition that they were of eruptive origin. It seems to us, on the 

 other liand, that these limestone occurrences are, very probably, similar 

 in character to those of Eastern Massachusetts, which are not a part of 

 the stratified formation, but rather of the nature of segregated masses, 

 or chemical precipitates, as will bo more fully set forth farther on in 

 this paper. 



Prof. A. R. Leeds, in a paper entitled "Notes upon the Lithology of 



the Adirondacks/' concluded 



" that the rocks of Essex County are part of the Norian Syfticm," and " that 

 these norites are a stratified rock, but have undergone a nietuniorphosis so 

 profound as to have caused them to he regar<led by Prof. Eumajns and earlier 

 observers a^s unstratified. The doleriies which are found of the same con- 

 stituent minerals, and are of tlie jnean si)ccilic gravity ol" these norites, liave 

 probably been formed from a portion of tliesc stratilled deposits by deeply 

 seated nietamorphic action, and have further tnodilied and greatly tilted the 

 superposed rocks in the course of their extrusion.^' (American Chcniisi, 18V7, 



VII., p. 339.) 



That these rocks belong to the Norian system was determined by 

 lithological evidence, which really means no more than this, that gab- 

 bros coming from difterent localities look somewhat alike. That the 

 rocks are stratified is, according to him, shown by the existence of a 

 more or less complete parallel arrangement of the constituent minerals. 

 Professor Leeds is a chemist, and not a pctrographer ; and since his 

 ideas are obviously simply a repetition of those of Dr. Hunt, his testi- 

 mony neither adds to nor detracts from the importance of the theoreti- 

 cal views of the latter, 



Mr. N. L. Britton, in 1881, in an article on the geology of Ilichmond 

 County, N. Y., (Annals of the N. Y. Academy of Sciences, 1881, IL, 

 pp. 1GI-I82,) advocates the view tliat the granite observed by him at 

 Tompkinsville is an Archtean metamorphosed rock. This granite is 

 said by him to be 'S^ery coarsely crystalline in structure," and no strati- 

 Beation is observable in It. No proof is furnished that it is of nieta- 

 morphic origin. 



