ON THE EFFECT'S OF LONG-CONTINUED HEAtf. 177 



pressure of which, at those great depths, is immense." " These considera- 

 tions," he further added, "will explain a great number of geological phe- 

 nomena ; " and he instanced those of hot springs, which he accounted for on 

 the supposition that rain-water in channels communicating from super- 

 ficial reservoirs with the interior of the earth, thence rises again, heated, 

 to the surface. 



Fourier, at the same time, expounded the methods by which, after extended 

 observation of the internal temperature, and further experiments on the 

 conduction of heat, he conceived that mathematic analysis might determine 

 the epoch at which the process of cooling began, concluding in the mean- 

 while from facts already known, — 1st, that no sensible diminution of tem- 

 perature has taken place during the period of historical chronology ; 2ndly, 

 that at a former era the temperature underwent great and rapid changes. 



Thus was a train of graduated causes, physical and chemical, introduced 

 into Geology on the foundation of inductive reasoning, which is capable of 

 resolving some of the chief difficulties of the science in our comparison of 

 the present with the past. 



When, for instance, we read in the organic contents of the strata the 

 history of a period when the climate was apparently uniform in all parts of 

 the earth, and learn from the imbedded plants that the temperature of Arctio 

 lands was once equal to that of warm latitudes at the present day, to account 

 for these circumstances, we need no longer bewilder ourselves with hypo- 

 theses ; we have a vera causa in the knowledge that the earth has passed 

 through a state in which its temperature was due, not so much to a sun then 

 veiled in clouds, as to a heat penetrating equally in all directions from the 

 centre to the circumference of the globe. 



When, again, we contemplate a mountain range, and view the abrupt pre- 

 cipices of some alpine chain, with its enormous masses of rock uplifted to 

 the clouds, and descending as many miles into the bosom of the sea, and 

 when we compare such abnormal labours of nature with the petty risings 

 of the earth's surface in the existing state of things, we have a vera causa 

 for that disparity, in the knowledge that there was a time when the eruptive 

 forces of the seething mass within were greater, and when a weaker crust 

 underwent vaster disturbances. 



Or if we examine the general structure of the strata, and see the same stra- 

 tum contemporaneously solidified over large portions of the earth's circum- 

 ference, and then observe the absence of consolidation in the actual opera- 

 tions of nature, whether under the pressure of deep seas, or elsewhere, 

 except in a few foci of igneous action, we have here also a vera causa 

 of the difference, in the ancient prevalence of that high temperature which 

 the laboratory of nature and art shows to be the most capable of lapidifying 

 stony materials. 



Descending into the details of mineralogy, we find the same departure 

 from the present order of nature in the constitution of minerals; and in the 

 sequence of chemical effects of heat increasing with the age of the stratum, 

 we see a real cause for the distinction. 



Thus, for example, to begin with the upper beds, the chemist knows that 

 solutions of carbonate of lime, at the ordinary temperature, deposit crystals 

 with the common form of calcareous spar, but near the boiling-point of 

 water with that of Arragonite. Now in the mineralogical collection of the 

 Yorkshire Philosophical Society is a specimen of this mineral investing 

 calcite, from the chalk cliffs of Beachy Head ; and if any one will examine the 

 caves of calcareous grit on the Yorkshire coast, he will find them in some 

 places lined, like those of volcanic rocks, or the mouths of hot springs, with 



1860. n 



