Sedimentary Rocks. - 69 



HV. Sandy Creek Road - Grits overlying » with some unconformity 



Diccllograptus shales. 

 V. Western Kororoit Ck. - 



(a) Eastern tributary Vertical Grits apparently conformable with 



Diccllograptus shales and seeming to 

 underlie them. The high angle of dip 

 makes deductions unreliable. 



(b) Main stream Thick-bedded fossiliferous sandstones and 



Diccllograptus shales unconformable 

 with Dicranograptus shales. 



The Riddell Grits — coarse and fine sandstones, with associated 

 Diplograptus shales, usually rubbly — seem everywhere to be 

 closely associated with Upper Ordovician shales. On the field 

 •evidence, and on the evidence of their graptolites, they might 

 well represent a shallow water phase of the Upper Ordovician. 



There is no doubt that the Grits overlie Dicranograptus shales, 

 apparently conformably. With the exception of the outcrop 

 along the Western Kororoit Creek, there is no evidence of beds 

 overlying the Grits conformably. Since along the Djerriwarrh 

 Creek Upper Ordovician shales seem to pass below Lower Ordo- 

 vician rocks, the result of faulting or overfolding, it is unsafe 

 to generalise and state that the Grits are interstratified with the 

 normal Upper Ordovician shales. The absence of overlying 

 beds throughout most of the area lends considerable weight to 

 the theory that they represent the last phase of the Upper Ordo- 

 vician, and mark the beginning of the change to the shallower 

 water conditions which prevailed during the Silurian period. At 

 any rate, the presence of Dicranograptus below the Grits would 

 seem to place them well up in the Upper Ordovician. 



(c) . Fossils other than Graptolites. 



Fossils are abundant in the Grits, but are poorly preserved as 

 •casts. Mr. F. Chapman, A.L.S., of the National Museum, Mel- 

 bourne, has identified the f ollowings forms : — 



(I.) " Dalrymple's," North-west of Red Rock, Gisborne. 

 (?) Plasmopora. 



cf. Stylaraea. 

 »(.?) Fenestella. 



cf. Eridotrypa. 



Leptaena, sp. 



Orthis, sp. 



