542 PROF. G. A. LEBOUR AND DR. J. A. SMYTHE ON [Aug. 1906, 



III. The Chemical Evidence. 



The Pebbles in the Upper Series. — These have been 

 described as occurring at many places — almost continuously 

 indeed — at and near the base of the Table-liocks Sandstone. At 

 times, they form a narrow band immediately or a few inches above 

 the unconformity ; or again they are found sparsely scattered through 

 a foot in thickness of the sandstone ; or, finally, they occur in such 

 numbers as to form a conglomerate many inches thick, as at G. 

 Plant-remains, evidently drifted, and a few shells (Carbonicola) are 

 also found, as well as angular and rounded pieces of shale and of 

 the soft fossiliferous parts of the Mussel-Band ; but well-rounded 

 pebbles of the harder parts of the Mussel-Band far outnumber the 

 rest of the included fragments of foreign material. The smaller of 

 these well-rounded pebbles are sometimes much oxidized ; the larger 

 are slabs several inches thick and measuring up to a foot in diameter, 

 with rounded edges, and containing the typical Car honicola-sh ells 

 irregularly distributed throughout the mass. 



Comparative determinations of the constituents of these pebbles 

 and of the mother-rock were made, with the following results : — 



I and II are samples of collections of small pebbles found at F and G 

 respectively. 



III is a big pebble from E. 



IV is from the Mussel-Band cropping out near Gr. 

 V is from the Mussel-Band cropping out near K. 



In sampling the last two, the harder parts were selected, as the pebbles 

 are mostly derived from these. 



I. II. III. IV. V. 



Loss on ignition 28-43 28-30 3074 3271 32"81 



Hygroscopic water F38 F39 153 0*88 071 



Combined water and | g. 21 2 . Q5 2AQ ^ ^ 

 organic matter j 



Insoluble in acids 11-51 1278 9*12 8*16 7*06 



A1,0 3 (soluble in acids) ... 1-65 0'40 2*44 T30 0"28 



S - 0-43 0-55 0-15 014 013 



P 2 0, 0-39 0-29 1-49 075 1-01 



MnO 0-92 0-97 1-29 1-56 1-35 



FeO 3562 3690 39-11 32-24 40-93 



Fe 3 1071 6-36 1-34 1-82 0-31 



CaO 205 448 4-60 1285 9-04 



MgO 3-04 4-00 4-36 3-93 200 



CD 25-80 28-96 31-15 3135 3271 



Alkalies (by difference) ... 1'29 0'87 102 0-96 053 



100-00 100-00 10000 10000 100-00 



The residue insoluble in hydrochloric acid from Sample III was found to 

 contain 22 - 56 per cent, of carbonaceous matter and combined water. The 

 ignited residue contained : — 



Si0 2 61-01 



A1 3 28-05 



Fe 3 4-38 



Cat) 0-10 



MgO 090 



Na 2 571 



10015 



