Rocks H ('<(!■ H''((.fIicote. 341 



scope the rock is seen to be more or less chertified, and to con- 

 tain numea'ous longitudinal and transverse sections of a tubular 

 organism, some of which are branched. The cross-sections are 

 circular, and show a central cavity now filled with chalcedony. 

 I am unable to determine the nature of these organisms. Small 

 circular bodies in tlie i-cjck are suggestive of the former presence 

 of Radiolaria. 



Anothei' section cut from the saime rock shows some triradiate 

 spicules, and other four rayed spicules intersecting at right 

 angles, which are referable to Frotosponi>ia. This is the first 

 record of fossils from the normal Ordovician rocks near Heath- 

 cote, but their evidence does not help much in fixing the age 

 of the series. Small circular areas similar to those described 

 above are seen in sections of some of the cherty shades of the 

 Dinesiis rocks, aind are also recognisable sometimes in an iron- 

 stained condition in some of the black cherts, as for instance 

 those near Gate 47, south of the Heathcote Railway Station. 

 It is possible that thej' may be inorgainic segregations of 

 chalcedony, but their defined boundaries and occasionally the 

 suggestion of an inner wall suggest an organic origin, and I have 

 doubtfully compared them to Radiolaria, whose structure has 

 be>en destroyed by seoondaiy silicificaition. It will be seen that 

 the palaeontological evidence from these rocks is still incon- 

 clusive, and it seems to me to be safer to continue to regard 

 them as of Lower Ordovician age until better evidence is forth- 

 coming. 



(c) The Age of the Black CJierts. — I have shown above that 

 these rocks were composed mainly of diabase' fragments, and 

 that their peculiar composition led to their almost complete 

 silicification. Their general agreement in dip and strike with 

 the Ordovicians, and the complete absence' of conglomerates 

 containing chert fragments between them and the Ordovicians, 

 points to their being the lowest part of the bedded Ordovician 

 exposed to view. At Lancefield, where cherts occur not only 

 between the diabase and the fossiliferous Ordoviijiaai, but also 

 interbedded with graptolite-bearing shales, their Lower Ordo- 

 vician age is clearly demonstrated. 



(d) The Age of the Diabase and other Igneous Rocks. — 

 Tlie field and microscopic evidence is not so complete- as to fix 



