10 



SHORTER CONTRIBUTIONS TO (iENERAL GEOLOGY, 1921. 



lations for the distance of this sand from the 

 base of unit C show: 



In the Rudd well 2,295 to 2,525 = 230 feet. 



In the Seaman well 3,185 to 3,040 = 455 feet. 



Ratio 230 : 455=1 : 1.9S. 

 The ratio of the distances of the sandstone from 

 the top of unit C is as follows: 



In the Rudd well 2,245 to 2,295 = 50 feet. 



In the Seaman well 3,045 to 3,185 = 140 feet. 



Ratio 50: 140=1: 2.8. 

 The much closer agreement of the ratio of 

 distance from the base of unit C than the ratio 

 of the distance from the top of imit C with the 

 ratio of the total thickness of the combinetl 

 units in the two weUs may indicate that the 

 upper boundary is jilaced too high in the 

 Seaman well. If the botindary between 3,070 

 anil 3,080 feet in the Seaman well is chosen, 

 then 3,075 to 3,185=110 feet, and the ratio 

 becomes 50 : 110=1 : 2.2 — that is, the ratio 

 from the top is almost identical with the 

 ratio of the total thicknesses. But in view of 

 the much more sandy deposition in the top of 

 unit C in the Seaman well than in the Rudd 

 well this agreement seems to me as much of an 

 argument against accepting the lower boundary 

 as favorable to it. Moreover, as the upper 

 boundaries of units are supposed to correspond 

 to more pronounced disturbances or interrup- 

 tions of sedimentation, it is in general to be 

 expected that the ratios of intervals from any 

 bed in the unit to the top of the unit will be 

 less regular than those of intervals from the 

 same bed to the base of the unit. 



One of the striking instances of parallelism 

 between the percentage logs of the two wells is 

 the similarity in the relations of unit C in both 

 wells. Ihifortunately the samples from 2,480 

 to 2,490 feet, from 2,500 to 2,510 feet, and from 

 2, .522 to 2,546 feet in the Rudd well are missing, 

 but there are enough samples to indicate that 

 the beds in both wells a little above the base of 

 unit C record a sudden invasion of a very sandy 

 fac'ics overlying a thin layer of deeper-water sed- 

 iments and immediately overlain l>y sediments 

 that were probably laid down in still deejier 

 water. In the Seaman weU the base of unit (" is 

 marked by a very typically ileveloped glauconi- 

 tic basal bed, more phosphatic than usual, almost 

 exactly similar material marks the base of 

 unit V, and between the two is a sharply 

 defined very sandy layer. In the Rtidd well 

 the base of ^mit (" is also marked bv a glau- 



conite and phosphate layer, and a very sandy 

 black limestone between 2,490 and 2,500 feet 

 appears to represent the sandy layer, but a 

 distinct base for unit C was not located. About 

 80 per cent of the sample from 2,490 to 2,500 

 feet is a rather coarsely sandy, coarsely cal- 

 careous glauconitic and phosphatic black 

 limestone or shale, but all the fragments ex- 

 amined appeared to have been formed above a 

 basal bed rather than as an actual basal bed. 

 In addition there were consideralde traces of 

 coarse rpiartz sand (1 millimeter or more in 

 diameter). Evidently a basal bed of unit (' 

 is present, but from the evidence summarized 

 above it can not be precisely located. The 

 basal beds of units C and V in the Seaman well 

 were the only ones not noted in the original 

 examination, probably on account of the black 

 color given to the fragments by the phosphatic 

 material, which seems to veil the glauconite. 

 For this reason and on account of the incom- 

 plete record in the Rudd well iniit (" has been 

 treated as essentially a part of unit ('. 



The respective depth relations of slude and 

 linu'stone discussed above (p. 3) are probably 

 well illustrated by a comparison of the com|)o- 

 sition of units C and C" in the two wells. The 

 Rudd well is in deeper-water deposits, and the 

 large amount of lime in the lower part of unit C 

 in the Seaman well has its eciuivalent in an ex- 

 ceptionally large amount of almost sand-free 

 clav in the Rudd well. Lime is more al)undant 

 in the upper ])art of unit C in the Rudd well, 

 corrt'sponding to the shallowing indicated by 

 tlie large amount of sand in the upper part of 

 unit in the Seaman well, and the shallowing at 

 the base indicated by the sand between 3,610 

 and 3,630 feet in the Seaman well is represented 

 by sandy black limestone in the midst of shales 

 in the Rudd well. 



UNIT D. 



Unit 1) i)erhaps more clearly than any other 

 unit in the two wells is correlatetl by the rela- 

 tion of its composition as illustrated in the per- 

 centage log to the composition of the units 

 above anil below it. In the percentage logs of 

 both wells it stands out as a sharply delined 

 unit, more argillaceous than the units below it 

 and diflering distinctly in the proportion of clay 

 from the unit above it. It is in both more 

 sandy and therefore was probably formed in 

 shallower water than most of the lower part of 



