Professor J. Johj — The Age of the Earth. 221 



especially to activities depending on molecular processes : prociesses 

 in wbich the mutual presence of the reacting substances is tbe 

 primary factor, tbeir rate of relative motion or circulation entering 

 tbe result only in a secondary manner. Tbe metbod, in sbort, 

 relies principally on uniformity in tbe prevalence of tbat most general 

 of geological conditions, tbe mutual presence of water and rock 

 material over tbe land areas. I can best explain by an example. 

 Suppose we desire to estimate tbe rate of solubility of basalt in 

 water. We arrange tbat a measured quantity of water circulates 

 over tbe fragments of rock for a certain time. Now in tbis 

 experiment, wbetber we circulate tbe water quickly or slowly 

 over tbe rock tbe result will be tbe same or nearly tbe same. 

 Tbis is so because tbe molecular actions are relatively so slow 

 tbat even very sluggisb circulation of tbe water suffices to renew 

 tbe solvent before saturation is nearly attained, and so suffices to 

 preserve tbe action at its maximum rate. Tbe accelerative influence 

 of friction — as in Daubree's revolving cylinders — plays relatively 

 but a small part in tbe work of cbemical and solvent denudation 

 on tbe earth's surface. 



But advantages depending on tbe restriction of our Uniformi- 

 tarianism are not the only ones wbich tbe method claims to possess. 

 The quantities involved, those on which our final answer depends, 

 are more clearly defined and more accurately measurable than those 

 required in Uniformitarian methods based on rates of sedimentation. 

 The total volume of the ocean, its composition, tbe volume and 

 composition of the river water, are quantities measurable loithoni 

 speculation ; our knowledge of which will grow with the advance 

 of Science. 



The value of this restricted Uniformitarianism may be exemplified 

 in tbe possibilities involved in tbe abnormal lunar tides suggested 

 by Professor G. Darwin. If such abnormal tides affected the earth's 

 surface within the period of the Geological Time of which we speak, 

 the mechanical effects would remain the chief record ; and we could 

 not say if the wider and barer coasts of the period would contribute 

 more or less tban the normal dissolved matter to the ocean. "We 

 might argue for more on the ground of increased mechanical action ; 

 for less, on the grounds that tbe soils wherein cbemical effects would 

 most favourably progress had not been formed. Very probably tbe 

 ultimate result would be to affect our numbers but little. 



This appropriately leads me to tbe question of the nature of the 

 primitive ocean. I submit tbat upon those who wish to imagine 

 the waters of the primeval earth charged with alkaline salts rests 

 the onus of showing hoAv these elements escaped the avidity of the 

 silica under early igneous conditions : the combination of the two 

 being tbe course of events which we prima facie infer. Or, if they 

 admit such formation of alkaline silicates, they have to explain tbe 

 subsequent release of the alkali. 



On tbis last point I have in my paper gone on the assumption 

 (justifiable, as I submit) that long-continued attack from free acid 

 cannot be assumed as directed to the one element sodium. Free 



