38 HORN EXPEDITION — GENERAL GEOLOGY. 



some of the eruptive dykes, at least those that appeared hxst, would 

 have penetrated the Ordovician strata. 



(c) There is an entire absence of fossils in the luetamorphic group, whereas 

 even the Lower Cambrian rocks of Yorke's Peninsula and tiie 

 Flinders Kange in South Australia, and of the Kimberley district 

 in West Australia, liave been proved to be fossiliferous. 



Tlie evidence obtained by us points to much of the metaniorphic group having 

 had an eruptive origin, whereas the Cambrian rocks of Australia, as far as at 

 present known, are entirely sedimentary. No definite correlation will be attempted 

 between this group of rocks and others of apparently the same nature elsewhere in 

 Australia, inasmuch as no test of contemporaneity or homotaxial origin has yet 

 been discovered for rocks of Pre-Cambrian age. Similarity of mineralogical 

 composition cannot be depended on as a basis of correlation even among Cambrian 

 and Post-Cambrian strata, and much less in the Pre-Candjrian. 



PaUeontological evidence obviously entirely fails us. Lastly, the test of its 

 stratigraphical relations, even had Cambrian strata been proved to overlie the 

 metaniorphic group unconformably, would have been inadmissible, in view of the 

 possible divisibility of the Australian Pre-Cambrian group, like that of North 

 America, into a number of sub-groups, separated from each other by strong uncon- 

 formabilities. 



A few words, however, on the Pre-Cambrian rocks of other parts of South 

 Australia may be of interest in this place. The best known and most important 

 developments of undoubted Pre-Cambrian rocks are to be found in Yorke's Pen- 

 insula and in the Mount Lofty Range and its N.N.E. extension. In the JNIount 

 Lofty Range, according to Prof. Tate,* the Pre-Cambrian rocks occupy a vast 

 monocline, dip to the S.E., and are not less than ten miles in thickness. 



The peculiar feature of tliese rocks is the greater degree of metamorphism 

 exhibited as we ascend in order. At the base clay-slates, quartzites, and lime- 

 stones occur, undoubtedly sedimentary rocks altered to a greater or less degree. 

 These pass upwards into mica-schist, gneiss, and even granite, rocks partly at least 

 of a probable eruptive origin. No explanation of this apparent anomaly has been 

 given. 



At Black Point, near Ardrossan, on the east coast of Yorke's Peninsula, true 

 Pre-Cambrian rocks occur underlying uncomformably limestones of Lower Cam- 

 brian age, containing a trilobite and coral fauna characteristic of that age. 



* Op. fit., i<. l". 



