74 TRANSACTIONS OF THE [JAN. 21, 
nitz’s Protogea, has been most widely believed. The critical 
stage in this method of development came when convection 
ceased and the sphere was all the same temperature, the stage 
usually called consistentior status. Then came the formation of 
a crust and the beginning of geological phenomena as usually 
discussed. The speaker had reason to question the reliability 
of the nebular hypothesis and whether the earth had ever been 
gaseous, etc. An origin for the globe and an explanation of its 
heat are perhaps as well to be found in the collision of meteoric 
bodies. 4 
Thetime that has elapsed since the consistentior status has been 
an interesting subject for computations, and widely varying es- 
timates have been made. Lord Kelvin in 1862, 0n very ques- 
tionable data, placed the limits of geological phenomena at 20,- 
000,000-400,000,000 years in the past. On the same line, Tait 
estimated 10,000,000, but it is doubtless true that in England 
the weight of Kelvin’s authority fettered geological thought in 
the last thirty years to too narrow limits of time, for no geolo- 
gist of eminence questioned his results. Yet within a month 
Lord Kelvin has raised his upper limit to a possible 4,000,000,- 
000. All must appreciate that if the data are unreliable, the 
finest processes of mathematics will lead to no certain result. 
The speaker concluded that to secular cooling must be attri- 
buted the principal motive force. The main criticism raised 
against it is its insufficiency, but George Darwin has shown that 
as a cause it can be mathematically shown to be able to produce 
results at least of the same order as those observed. In the 
speaker’s estimation it is probably sufficient, although the heat 
radiated is a very difficult thing to measure in a reliable way. 
Our data are all from the continents, and they have not been ob- 
tained in sufficient quantity. The oceanic areas are necessarily 
unobserved. 
In discussion Professor Kemp stated that attention had natur- 
ally been drawn to the interior of the earth in the endeavor to 
explain, first of all, the contrasts of the continental elevations 
and the oceanic abysses, and secondly, the crumplings, foldings 
and faults of mountainous regions. Herschel’s explanation, 
