65 



^'Half-way Hill" (otli&rwise called the ''Big Hill"). At 200 

 yards up this hill there is a quarry in shales that exhibit 

 a small syncline, or kink, in the beds, ending in a dip 

 at 20°, Half-way up the hill the beds consist of thin 

 dolomitic limestones, separated by earthy r»artings, the latter 

 being indurated by cementation show differential weathering, 

 and stand out from the limestones in relief : dip N.E. at 40°. 

 In the upper part of the hill, on the road, the dolomitic beds 

 become thicker and are separated by shaly partings : dip N. 

 10° E. at 42°, Near the top of the series are Archaeocya- 

 thinae beds, 



Quartzites are on the northern side of the great dolomitic 

 belt, and these are succeeded and intercalated with more 

 dolomitic beds. 



[For descriptions of the section from the ''Big Hill" to 

 Wirrealpa, see under Section XV., as that part of the journey 

 was made from Wirrealpa.] 



IX. Wirrealpa and Neighbourhood. 

 The Wirrealpa Head Station stands on purple sandstone 

 flags which underlie a series of thin-bedded limestones. The 

 general strike of the country is north-easterly, with a south- 

 easterly dip. Behind the station house, soft decomposing flags 

 can be seen' in the small creek, with a dip E. 20° S. at 70,°, 

 the beds making a curve round at the homestead. Within a 

 short distance of the house, bands of oolitic limestone occur 

 in calcareous and sandy shales. These bands are of much 

 interest, as they include layers, up to a few inches in thick- 

 ness, of broken and thickly-matted shells of Oholella, 

 Pteropods, and Trilobites. These beds have 'every appearance 

 of being shore deposits, their oolitic structure and the frag- 

 mentary condition of the organic remains, closely matted 

 together, all point in that direction. Associated with the 

 same beds are some very fine-grained and laminated sandy 

 layers, which show worm burrows and casts; the burrows are 

 in the form of vertical tube-like passages, while the worm- 

 casts are seen on the flat surfaces of the slabs: dip S, 20° E, 

 at 70°, At a slightly lower position in the series is a remark- 

 able layer of limestone, up to 6 in. in thickness, which is 

 thickly crowded with flattened and spheroidal nodules of 

 Girvanella, up to an inch and more in diameter. Their 

 determination was made by thin microscope sections by which 

 the typical structure of this organism was shown. Some of 

 the nodules thus examined, however, failed to give a clear 

 definition of structure; the very minute form of the tubes 

 had, by molecular rearrangement, become more or less blended 

 with the matrix. 



