Edward A. Martin—“ How Long Ago” in Geology. 351 
the Old Red Sandstone took 136,500,000 years to arrive upon the 
scene, and the small reptiles of the coal era were the outcome of 
159,600,000 years. The winged reptiles of Jurassic times took 
21,875,000 years more to be evolved, whilst the small marsupial 
mammals of the same period were followed in another 16,940,000 
years by the great mammals of Eocene times. And then came the 
crowning of the evolutionary movement by the appearance of the 
human species in Phocene times. 
ACTUAL . 
BEFORE RELATIVE - 
oe HOS ICNESS ComPpREsSION.| PROPORTION. — 
IN FEET. 
Pleistocene and Recent... 4,000 4,000 4 2,800,000 
Pliocene ... Hae ae 5,000 5,000 5 3,500,000 
Miocene ... tes sis 9,000 9,000 9 6,300,000 
Oligocene aos ae 12,000 13,200 13°2 9,540,000 
Tecan | A eee eee 12,000 13,200 13-2 9,540,000 
Cretaceous aie aes 14,000 15,400 15°4 10,780,000 
Jurassic ... es a: 8,000 8,800 8°8 6,160,000 
"each, aul eee alas 13,000 16,250 16-25 11,375,000 
Permian kek) ks 12,000 15,000 15 10,500,000 
Carboniferous... ac 24,000 30,000 30 21,000,000 
Devonian eh she 22,000 338,000 33 23,100,000 
Sinn a a aes 15,000 22,500 22°5 15,750,000 
Ordovician wie sets 17,000 25,500 25°5 17,850,000 
Cambrian aes eae 16,000 24,000 24 16,800,000 
Keweenawan ... ie 50,000 75,000 75 52,500,000 
Penokee ... ahr S53 14,000 21,000 Dik 14,700,000 
Huronian RE 18,000 27,000 27 18,900,000 
265,000 357,850 357°85 251,095,000 
In the above table notice has been taken only of actual strata 
in calculating the various ages, and no mention has been made of 
the great breaks in life-history which are noticeable in studying 
fossil remains, and these breaks may—indeed, in some cases must— 
represent great periods of time. Their actual duration could only 
be arrived at by discussion and agreement among geologists, but it 
is of course well recognized that the greatest breaks in the continuity 
of life occurred between the Permian and the Triassic systems and 
between the Cretaceous and the Eocene.’ The very fact, however, that 
different names have been necessary in alluding to the systems suggests 
a possible break between each, and presuming that we must confine 
ourselves to about 250,000,000 years, as already shown, we must find 
room for the gaps during which no strata were deposited, by deducting 
some of the years allotted to each formation.* 
1 The principal anconformities have been considered and estimated for by the late 
Mr. J. G. Goodchild in his ‘‘ Evidence regarding the Age of the Earth’’ (see 
Review in Grou. Mac., 1897, pp. 415-417), Edinburgh, McFarlane & Erskine, 
1897, and Proc. Roy. Phys. Soc. Edinburgh, vol. xii, pp. 260-303. 
2 Mr. Goodchild liberally allows 70,200,000 years for three well-recognised breaks 
in his geological series, and for the whole period of geological time he suggests 
704,235,000 years. 
