THE LOWER HURONIAN. 339 



directions parallel. Many of these have been added to hj secondary 

 growths of massive hornblende or of fibrous actinolite. This addition of 

 the secondary material only tends to emphasize the parallel arrangement 

 of the particles, since the greatest addition has been made on the ends of 

 the fragments. This was noticed in some of the graywackes made up 

 almost exclusively of feldspar and hornblende, with mica next in abun- 

 dance, and very little quartz. In such rocks the biotite alters to chlorite. 

 Alteration of the feldspar with the production of new minei'als also takes 

 place, and a few quartz grains alone remain to give evidence of the clastic 

 character of the constituents. When such rocks take part in orogenic 

 movements the quartz may be crushed, and in general a better degree of 

 schistosity produced than previously existed, and as a result of such move- 

 ments hornblende-schists may eventually be produced. The banding of 

 these hornblendic sediments has been referred to. These bands of finer 

 and coarser materials have essentially the same composition. There also 

 appears to be a relation between the fineness of the hornblende grains of 

 the original sediments and the character of the new amphibole. Thus it 

 was noticed that in the alteration of the very fine-grained sediments the 

 new amphibole is added in the form of fine actinolite needles, whereas in 

 the coarser graywackes the new amphibole is in general a massive horn- 

 blende. The final product of the metamorphism of these rocks would 

 probably retain this essential difference, so that we would get fine- and 

 coarse-grained ampliibole-schists, or possibly banded actinolite and horn- 

 blende-schists. 



There is also a banding due to the separation of the kinds of minerals. 

 Thus there will be some dark bands made up essentially of hornblende and 

 mica with but little feldspar, and alternating with these bands there will 

 be bands of feldspar with but little hornblende or biotite. When such 

 rocks are metamorphosed there will be no very great migration of material 

 from the one band to the other, and certainly the original differences in the 

 bands will be shown to a certain extent in the difterences in the bands in 

 the metamorphic product. Presumably the final product would be an 

 amphibole-schist complex made up of alternating bands of amphibole- 

 schists rich and poor in feldspar or other secondary products — quartz and 

 feldspar, perhaps — derived from the original feldspar and of different color, 

 corresponding to the difference in mineral composition. 



