JOSEPH FOURIER. 163 



that of their superposition. The deepest liave been formed at the most 

 remote epochs. The attentive study of these different envelopes may 

 aid us in ascending the stream of time, even beyond the most remote 

 epochs, and eidightening ns with respect to those stupendous revolu- 

 tions which iieriodically overwhelmed continents beneath the waters of 

 the ocean, or again restored them to their former condition. Crystalline 

 rocks of granite upon which the sea has effected its original deposits 

 have never exhibited any remains of life. Traces of such are to be found 

 only in the sedimentary strata. 



Life appears to have first exhibited itself on the earth in the form of 

 vegetables. The remains of vegetables are all that we meet with in the 

 most ancient strata deposited by the waters; still they belong t<^ plants 

 of the simplest structure — to ferns, to species of rushes, to lycopodes. 



As we ascend into the upper strata, vegetation becomes more and 

 more complex. Finally, near the surface, it resembles the vegetation 

 actually existing on the earth, with this characteristic circumstance, 

 however, which is well deserving attention, that certain vegetables 

 which grow only in southern climates — that the large palm-trees, for 

 example — are found in their fossil state in all latitudes, and even in the 

 center of the frozen regions of Siberia. 



In the primitive world, these northern regions enjoyed then, in winter, 

 a temperature at least equal to that which is experienced in the present 

 day under the parallels where the great palms commence to appear ; at 

 Tobolsk, the inhabitants enjoyed the climate of Alicante or Algiers. 



We shall deduce new proof's of this mysterious result from an atten- 

 tive examination of the size of plants. 



There exist, in the present day, willow-grass or marshy rushes, ferns, 

 and lycopodes, in Europe as well as in the tropical regions; but they 

 are not met with in large dimensions, except in warm countries. Thus, 

 to compare together the dimensions of the same plants is, in reality, to 

 compare, in respect to temperature, the regions where they are i)ro- 

 duced. Well, place beside the fossil plants of our coal mines, I will not 

 say the analogous plants of Europe, but those which grow in the coun- 

 tries of South America, and which are most celebrated for the richness 

 of their vegetation, and you will find the former to be of incomparably 

 greater dimensions than the latter. 



The fossil flora of France, England, Germany, and Scandinavia offer, 

 for example, ferns ninety feet high, the stalks being six feet in diameter 

 or eighteen feet in circumference. 



The licopodes which, in the present day, whether in cold or temperate 

 climates, are creeping-plants, rising hardly to the height of a decimeter 

 above the soil; which, even at the equator, under the most favorable 

 circumstances, do not attain a height of more than one meter, had in 

 Europe, in the primitive world, an altitude of twenty-five meters. 

 One must be, blind to all reason not to find in these enormous dimen- 



