332 



THE AZOIC SYSTEM AKD ITS SUBDIVISIONS. 



of the group, but whether few or many, they are always separated by beda 

 of gneiss which in no way differs either in constituent quality or diversity of 

 arrangement from the gneiss lower down, excej)t in regard to the presence of 

 accidental minerals, the most common of which arc garnets." (/. c, pp. 41^ 42.) 



It is thus seen that his divisions arc arbitrary and theoretical, both 

 being, according to his statement, conformable and intcrluminatcd with 

 one another. As regards the origin of the " syenitic gneiss," or lower 

 formations, he writes that they possess ''an aspect inducing a theoreti- 

 cal belief that they may bo ancient sedimentary formations in an altered 

 condition." (/. c, p. 40.) The lamination planes of the gneiss (?) ap- 

 pear to be taken without hesitation as planes of sedimentation. As 

 before, theoretic belief, and not evidence, was the basis on which all 

 was decided, and Logan never went beyond this. 



Without adopting any theory of the origin of the rocks in question, 

 it is sufficient simply to point out that, accepting Logan's own state- 

 ments as true, the rocks might, so far as the jiublished evidence goes, 

 have originated in any way not a priori impossible. Bis evidence is 

 valueless excepting so far as credit may be given to the skill he may at 

 that time have possessed in distinguishing metamorphic sedimentary 

 from metamorphic eruptive rocks. 



Later he stated : — 



" The succession of rocks in ascending order, .... after crossing sixty-three 

 miles, .... occupied by the unbroken uidformity of the lower metamorphic, 

 or syenitic gneiss, formation, is as follows : — 



" 1. Chloritic slates and conglomerates. 



" 2. Greenish sandstones. 



" 3. Fossiliferous limestones." (/. c, p. 67.) 



The chloritic slates and conglomerates were said to nold pebbles and 

 boulders of the subjacent gneiss. The limestones were regarded from 

 their fossils as being of the age of the Niagara. Mr. Logan says ; 



" The facts that have aa yet come within my observation in res])ect to these 

 formations have not been sufficient to enable me to determine to my own satis- 

 faction what their relations are in respect to conformability. That the lime- 

 stones are unconformable with the slates appears almost certain, but it is not 

 in my power to state with which the intermediate sandstones are conformable, 

 if they are so with either, or whether tliey are unconformable with both ; nor 

 can I assert whether the slates are conformable with the gneiss." (/. c, p. 69.) 



i 



Wo thus see that the chloritic slates and conglomerates, which later 

 on lithological evidence were referred to the TTuronian, were only shown 

 to be older than the Niagara, their true age being unknown. 



