12 



SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1921. 



woUs. In the Seaman well sample from 

 .1, !)()() to 3,970 feet occurs a peciiliai- white to 

 light-hrown or gray shale with minute bro\\^l- 

 black spherules, 0.1 to 0:2 millimeter in diam- 

 eter. Under the microscope the material is 

 seen to be very finely micaceous or sericitic, 

 with varying amounts of ratlun- coarse sand. 

 Th(^ spheruU^s are brown to almost ojjaque, are 

 weakly birefringent, and liave a vaguely radial 

 structure, in some surrounded liy a concentric 

 shell of suniiar substance. At the center of 

 many of them is a small sulphide concretion. 

 They are insoluble in nitric acid, and no test for 

 phosphorus could be ol)tained after fusing them 

 with sodium carbonate. It is hoped later to 

 determine their nature. Some of the features 

 of the matrix suggest a volcanic origin, but no 

 volcanic glass or unusual numbers of heavy 

 minerals were noted on microscoj)ic inspection. 

 Material of this general type, much of it merely 

 white shale without black sjiherules. was found 

 distributed through the section in the Seaman 

 well from this uppermost occurrence in the 

 sample from 3,lt6() to 3, '.170 feet to fragments in 

 the sample from 4,165 to 4,180 feet — that is, 

 in units G. H, I, and J. This distribution with- 

 out regard to lithologic facies or apparently to 

 any clear boundary is one of the factors favor- 

 ing the belief in a volcanic origin. In the Rudd 

 well the only distinct occurrence noted was in 

 unit H between 2,780 and 2,790 feet. 



The only show of oil recorded in the driller's 

 log of the Seaman well is in unit G in the inter- 

 val between 3,960 and 4,010 feet, but the e.xact 

 depth is not given. The horizon at which it 

 would seem most likely to occur would be that 

 of the coarse glauconitic basal sandstone of unit 

 G, just below 4,010 feet, which, as indicated in 

 the generalized log (column 6, PL I) is believed 

 to be the ecjuivalent of the Ranger sand. 



UNITS H AND I. 



Units H and I are grouped together because 

 they stand out clearly from the units above and 

 below them by being more argillaceous and 

 generally containing more detrital material. 

 In the j)ercentage logs of both wells there is also 

 a clear maximum of clay in unit H. Both 

 imits in both wells show two maxima of sand. 

 The lower boundary of unit I is sharply defined 

 in the Rudd well, not only by a well-developed 

 glauconitic bed but also by a sharp and pro- 

 nounced change, shown in both the percentage 



log and the synthetic log, from the calcareous 

 material that prevails below it to the more ar- 

 gillaceous material above. In the percentage 

 log of the Seaman well. there appears the same 

 sharp increase of shale accompanied by a basal 

 accumulation of sand, but the srathetic log of 

 the Seaman well does not show the sharp litho- 

 logic boundary, gray limestones being repre- 

 sented as extending into the lower part of unit 

 I. In the sample from 4,090 to 4,100 feet in 

 the vSeanian well, in which the highest gray 

 limestone in unit I appears, traces of very 

 coarse (juartz sand with a very few fragments 

 of coarse sandstone like that at 4,072 feet were 

 found, but the scarcity of these fragments and 

 the lack of a definite boundary here in the per- 

 centage log make it seem probable that they 

 were derived 1iy caving from beds above. The 

 sample from 4,126 to 4,130 feet in the Seaman 

 well also shows large traces of cpiartz sand, l)ut 

 no glauconite coidd be found associated with 

 them. The boundary chosen as the base of 

 vmit I is therefore ]irobably the correct one. 

 Probably units II and I together as they appear 

 in the percentage log of the Seaman well record 

 an oscillation, a rise followed by a fall of base- 

 level between units J and G similar to that be- 

 tween units C and B, but the sharp change of 

 facies between imits J and I indicates that here 

 the rise of base-level was not continuous from 

 the underlying unit. The upper part of unit 



I and the lower part of unit II, which were de- 

 posited during the period of greatest elevation 

 of base-level, contain several layers with glau- 

 conite, sulpiride, and sand. 



To conform with the l)Oundary between 

 units P» and 0, the boundary between units H 

 and I in the Seaman well should be taken at 

 4,04.5 feet, the approximate position of the aki- 

 netic siu'face, but on account of the greater 

 practical availability of a lithologic boundary 

 and of uncertainty as to the position of the 

 akinetic surface due to the mixed composition 

 of even individual small chips in this part of the 

 section, I have chosen the coarse glauconitic 

 bed shown between 4,068 and 4,072 feet in the 

 s\Tithetic log as the boundary between units 



II and I. In the sample from 4,060 to 4,070 

 feet there is about 20 per cent of black calca- 

 reous, somewhat glauconitic and very sul- 

 pliicUc sandstone, containing some of the 

 coarsest sand grains noted in any part of the sec- 

 tion. But an entirely similar sandstone occurs 



