36 HORN EXPEDITION — GENERAL GEOLOGY. 



coarse granite." He also points out that they show " signs of stratification " and 

 " dip at varying angles." Th" ju-csence of quartz reefs is also mentioned by the 

 same author-, and in a later portion of the same report a detailed description of the 

 principal alluvial diggings, and auriferous reefs in the vicinity of Artunga is 

 given. 



Mr. Chas. Chewings (xi., p. 247) calls the series of rocks under consideration 

 Pre-Silurian. This he did on the evidence of their unconformability and inferior 

 stratigraphical position to rocks containing fossils ascribed by Prof. Tate to the 

 Upi^er Silurian. This was, of course, under the circumstances, a safe provisional 

 conclusion. There are, however, many weighty reasons why, in the light of our 

 more extended knowledge of them, they should now be more definitely termed 

 Pre-Cambrian. He asserts also that they are " distinctly stratified, with a dip in 

 general to tlie. north at a steep angle." He next gives what he considers to be 

 the order of succession of the rocks, commencing from the north side of the 

 McDonnell Ranges, as follows : — Chlorite-schist, granite, " micaceous schists and 

 metamorj^hic granite, with occasional outcrops of coarse eruptive granite and 

 other eruptive rocks," quartzite, " metamopliosed clays and shales, interstratified 

 with yellow and blue crystalline limestone." 



Mr. H. Y. L. Brown (xii., p. 12) points out that, overlying unconformably "the 

 crystalline, metamorphic, gneissic, and granitic Archaean rocks of the McDonnell 

 Ranges, there are two other rock systems, unconformable to each other," which he 

 calls respectively Cambrian and Lower Silurian. In a later report (xiv.) he calls 

 these metamorphic rocks Archsean, a name which for many reasons it would be 

 better to replace by Pre-Cambrian. 



Prof. Tate, in referring to the Pre-Canibrian rocks of Australia in his 

 Inaugural Address to the Australasian Association for the Advancement of Science 

 in 1893,* thinks "that there are good reasons for the belief that these rocks, which 

 exhibit the phenomenon of regional metamorphism, belong to one epoch ; " and he 

 goes on to say that "the chief evidence" (for the above statement) "is that they 

 occupy parallel lines of elevation, having an approximate north and south bearing." 



A uniform meridional trend, however, in the axis of folding of regionally 

 metamorphosed rocks does not appear to be a safe guide as to the Pre-Cambrian 

 age of all such Australian rocks as exhibit it, as the trend of the lines of elevation 

 and foliation occupied by the metamorphic rocks of tlie McDonnell Ranges are 

 nearly due east and west, and it is now known that these rocks are Pre-Cambrian. 



Rep. Austr. Assoc. Adv. Sci., Adelaide, 1893, p. 45. 



