SCIENCE-GOSSIP. 



79 





Feet. 



Kon. 



L.C. eon 



Longmyncl group . 



• 3.75°— 5. 00 ° • 



. Il6 



1 



,, 



. 5,000 — 6,250 . 



• "5 



2 



,. ,. 



. 6,250—7,500 . 



. 114 



•• 3 



Menevian 



. 7,500 — S,ooo 

 1 — 600 



113 



•• 4 



L. Lingula flags 



1 — 1,000 . 



. 112 



•■ 5 



n n 



. 1,000 — 2,000 . 



. Ill 



.. 6 



Mid. Lingula flags . 



. 2,000 2,500 



I— 500 



• no 



•• 7 



„ • 



. 500—1,500 . 



. I0(J 



.. 8 



Up. Lingula flags . 



. 1,500 — 2,000 



I— 500 



500 — 600 



■ ro8 



| 



.. 9 



Tremadoc 



I 1,000 



- 107 



. . 10 



Arenig 



I — 200 



) 





In America the standard column is provisionally 

 based on the Eureka section in the State of Nevada. 

 The lowest bed is a quartzite, and is at present 

 assigned to the Huronian period. The time-valuing 

 of the other beds is given below. 



Prospect Mt. limestone 



Feet. 



Eon. 



1— 500 . 



. 116 



500 — 1,000 



• 115 



. 1,000 — 1,500 



. 114 



. . 1,500 — 2,000 



■ 113 



. . 2,000 — 2,500 



112 



. . 2,500 — 3,000 



in 



. . 3,000—3,050 

 1 — 900 



) 



• no 



900 — 1,600 

 1— 150 



) 109 



150— 650 . 



. 10S 



650 — 1,150 



107 



Secret Canon shale 



11 11 ji 



Hamburg limestone 



By way of showing how the stratigraphic grade 

 scale can be used for the purpose of indicating the 

 time correlation of strata, based on stratigraphic 

 considerations, a few sections have been summarised 

 on the chart form appended. The time grade is 



shown at the bottom together with the number of 

 the eon ; the stratigraphic grade and the number of 

 each i.ooo feet of clay are given at the top ; the 

 figures are precisely the same, but they have 

 different meanings. The grade numbers occupy 

 much space in the table, but it should be borne in 

 mind that those given refer only to the latest 

 moment of the eon, or to the latest bed of the 

 i.ooo feet to which each respectively belo.igs. The 

 eonic numbers refer to all the space representing 

 the eon ; the asterisk corresponds to a position 

 about midway in eon 115. 



The same facts could be tabulated by giving the 

 names of the divisions and adding the stratigraphic 

 or the eonic range. For instance, the Pembroke- 

 shire beds, as tabulated below, can readily be 

 compared with the sections given in the chart. 



(As these scales are probably new to the reader, 

 a few remarks on the way of reading them may 

 obviate some confusion. The larger figures, those 

 of the grades, it will be noticed, increase as we 

 proceed from left to right, that is, the scales 

 commence with the Laurentian and end with the 

 present period. Thus 440,000 at the top of the 

 Menevian means that forty-four per cent, of 

 geological time as represented by strata had then 

 lapsed, and fifty-six per cent, was to come. It also 

 means that forty-four per cent, of the geological 

 column had been laid down and that the other 

 fifty-six per cent, was as yet non-existent. 

 The smaller numbers increase from right 

 to left, because they start from the present 

 and extend backwards in time, or from the 

 surface deposits downwards. Thus 113 means 113 

 eons ago, as regards time, and that if all the beds 

 were clay, had been continuously deposited, and 

 had retained their original horizontality, the bed at 

 the' top of 113 would be 112,001 feet below the 

 surface, and would correspond to 112,000,001 years 

 ago.) 



LOWER CAMBRIAN (LOWER TACONIC). 



420,000 425,000 430,000 435,000 440,000 445,000 450,000 455,000 460,000 465,000 470,000 

 116 115 114 113 112 in no 109 108 107 



t j/- Sc ... , rl Mid. Lingula _: an £ 6 = 



Longmvnd Group. 3 nj L. Lingula Flags. trior™. • rt S ° o 



a -5 Fla = s - gs $* a 



Wales || || || II il 



Coldbrook Beds. St. John Group. 

 New Brunswick || || 



Nevada— 



Prospect Mount. Limestone (Beds 2 to 22) Limestone (No. 23 Bed). 

 Highland Range ]| II 



Prospect Mount. Limestone. ^Hiate ° D Hamburg Limestone. 



Eureka ^ | ! 



116 115 114 113 112 in no 109 108 107 

 )2o,ooo 425,000 430,000 435,000 440,000 445,000 ' 450,000 455,000 460,000 465,000 470,000 



