416 Bevieivs — Goodehild's Age of the Earth. 



liad been formed. For all his calculations the author details the 

 stateraeuts, statistics, and opinions advanced by many observers. 

 The mode of formation and rate of growth of marine limestones are 

 carefully estimated, and one foot in 25,000 years is taken as a fair 

 rate to allow for the formation of marine limestones other than 

 coral-reefs. The Nnmmnlitio Limestone, if only 3,000 feet thick, 

 required no less than 75,000,000 years for its formation. Thus, 

 a total of 93,420,000 years must have elapsed between the commence- 

 ment and the close of the Tertiary Period. 



In like manner the author calculates the time required for the 

 formation of the Chalk and other Cretaceous strata, explains his 

 views of the relative time-value of the tilting and denuding 

 necessarily associated with unconformities, and proceeds to the 

 consideration of the other Mesozoic formations, and those of the 

 Upper and Lower Paleeozoic times. His remarks on the Carboni- 

 ferous Series are noteworthy. Very different are the estimates 

 that have been made for the time necessai'y for the production of 

 a foot of coal — thus, by Huxley 500, Boussingault 3,600, Phillips 

 1,530, Croll 1,600, Humboldt 1,800 years. 



These suppositions are for the terrestrial origin of coal ; but 

 Mr. Goodchild thinks that some coal-seams may have been sufficiently 

 marine to allow of an average estimate of one foot in 3,000 years. 

 At all events, for the 105 feet of coal-seams near Manchester he 

 would give 315,000 years. This, with 10,500,000 years for the 

 7,000 feet of Carboniferous sandstones (at one foot in 1,500 years), 

 and 21,000,000 years for 7,000 feet of Carboniferous shales (at 

 one foot in 3,000 years), makes up the sum for the Upper 

 Carboniferous Group. 



The author's summary of the time required for the knowa 

 geological series is as follows : — 



Time in Tears. 



For the Tertiary Period 93,420,000 



For the formation of the Chalk, Upper Greensand, Gault, 



and Lower Greensand 31,400,000 



Pre-Cretaceous Unconformity in Britain ... ... ... 13,200,000 



Time required for the deposition of the Jurassic-Wealden 



Series 59,400,000 



Time represented by the Tyrolian and Panormian (together 



comprising our 2>-irtrs and P<?nwi«w) rocks ... ... 87,500,000 



Unconformity at the base of the Lower New Eed in Britain 45,000,000 

 Duration of the Upper Carboniferous Period in Britain ... 31,815,000 

 Time required for the formation of 2,500 feet of Car- 

 boniferous Limestone ... ... ... ... ... 62,500,000 



Time represented by the Continental Devonian Limestones... 125,000,000 

 Duration of the period represented by the Salopian (Silurian) 



rocks 56,000,000 



Chronological value of the Unconformity at the base of the 



above 12,000,000 



Time required for the accumulation of the Upper Ordovician 



rocks 12,000,000 



For the Lower Ordovician rocks 33,000,000 



For the Upper and Middle Cambrian rocks 36,000,000 



For the Lower Cambrian rocks 6,000,000 



704,235,000 



