ARCELEAN GROUP. 265 



of the later strikes, are also materially contaminated with intrusions (and per- 

 haps extrusions) of an age prior to the deposition of the next succeeding sys- 

 tem. The fundamental gneisses and the Long Mountain basic series have 

 now no easily recognizable traces of sedimentation, and it is possible that 

 these rocks really represent extrusions or intrusions of one or more epochs 

 antecedent to the deposition of the Bodeville strata. I do not feel competent 

 just now to support by detailed evidence my own leaning towards a contrary 

 opinion, and the more especially since such high authority as Mr. A. C Law- 

 son has claimed a minor value in his district for some such facts as could be 

 presented from present knowledge of our area.* 



Although there are features described by him in his district which do not 

 seem to tally with the observations made in Central Texas, there is so much 

 of detail in his work and so little nicety of calculation in my own, that it is 

 to the interest of science to draw conclusions warily. This much may be 

 said, however, that nothing has yet been observed in our field which indicates 

 anything but an inferior position for the gneisses with respect to the basic 

 series, f Mr. Lawson's case is apparently a different one, unless it be discov- 

 ered that the granites and pegmatites in the trend of the Burnetan System 

 are really extrusions of later date, but "concomitant with the folding," as in 

 the Keewatin Series of British America. J 



That some of the interbedded igneous rocks are intrusive does not admit 

 of doubt; for they are compressed themselves, and in many cases the adjacent 

 schists are materially altered along the edges of the dikes. The ponderously 

 crystalline "squeezed" feldspar (orthoclase) and the distorted quartz crys- 

 tals of the Barringer Hill in Llano County are marked examples of the former, 

 and numerous instances might be given of the latter effect. So far as my 

 observation goes, these dikes are not confined to one portion of the Burnetan 

 System, but they seem to transect all three series. Such variations and local 

 manifestations as have been noted do not appear to require more explanation 



*At page 67 CC of vol. I, 1885, Annual Report of the Geological Survey of Canada, the 

 author remarks that "the dipping of the schists in opposite directions towards each other 

 does not necessarily imply a synclinal structure." I have based my opinion in a measure 

 upon such a structure in Central Texas. My own impression from Lawson's report is that 

 the two cases are dissimilar. 



fin these remarks the writer must not be understood as making any serious attempt to 

 harmonize the record in two widely separated Archaean areas, which may have had a simi- 

 lar history, but which have not yet been brought into true relationship and can not be prop- 

 erly compared, except by a vast amount of investigation in the intermediate territory. But 

 as a valid excuse for delaying conclusions, the bare possibility of such parallelism, in view 

 of the facts, may reasonably be adduced. 



JLawson, loc. cii, p. 100 CC. 



