. G. K. Gilbert — Inculcation of Scientific Method. 297 



To evaluate the effect produced under the second hypothesis 

 (the hypothesis, that is, that the geoid represented by the water 

 surface of Lake Bonneville has been deformed by the with- 

 drawal of the attraction exerted by the water itself) it is neces- 

 sary to employ mathematical analysis of a high order. As my 

 schooling in mathematics did not qualify me to undertake this, 

 I submitted the problem to an eminently competent colleague, 

 who has solved it rigorously and deduced for the deformation 

 of the geoid within the area of Lake Bonneville a maximum 

 amount of two feet. The second explanation is therefore elim- 

 inated from consideration, because quantitatively insufficient. , 



It remains to consider the rise of the isogeotherms, and to 

 evaluate the resulting elevation of the basin. It has been es- 

 tablished by numerous observations that in all lakes having a 

 depth as great as 1000 feet, the temperature at the bottom is 

 about 39° F. This depends upon the fact that water at that, 

 temperature is heavier than at any other, and having once 

 reached the bottom of a deep lake, it is withdrawn from the 

 circulation to which the upper layers are subject, and remains 

 undisturbed. The meteorological records show that the mean 

 annual temperature of the desiccated basin of Lake Bonneville 

 at the present time is 52°. The cnange from a humid to an 

 arid condition has therefore raised its temperature 13°. The 

 temperature of the surrounding regions has at the same time 

 undergone a change, of which we have no precise estimate. 

 The epoch of Lake Bonneville was the Glacial Epoch, and the 

 local climate was then in all probability cooler. If it was 13° 

 cooler, the isogeotherms would be no more affected at the center 

 of the basin than at its margins, and there would be no differen- 

 tial elevation. If it was cooler by less than 13° a differential 

 uplift would occur. For the sake of giving this uplift a 

 maximum value, we will assign a very small figure to the 

 general change of temperature, namely 3°, and assume that 

 the differential change with respect to the basin was 10°. A 

 formula devised by Fourier enables us to estimate the rise of 

 the isogeotherms, if only we know the conductivity of the ma- 

 terial of the earth, and the time which has elapsed since the 

 Bonneville shore line was carved. Then, if we know addition- 

 ally the rate of expansion of rock for a degree of temperature, 

 we are able to estimate the upheaval. Sir William Thompson 

 has determined experimentally a coefficient of conductivity. 

 The late Prof. Bartlett, of West Point, has determined the coeffi- 

 cient of expansion for several building stones, which may be as- 

 sumed to represent the crust beneath the Bonneville basin. 

 We do not know how these coefficients are affected by high 

 temperatures and great pressures, such as exist deep in the 

 crust, and an element of uncertainty attaches for that reason. 



