188 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



It is not very long ago, far within our own time, since geologists 

 spoke and wrote of chaotic fluids holding mineral matter in solution, 

 and of precipitations of crystalline rocks from that menstruum. But 

 these hypotheses, not only unsupported by, but at variance with all 

 known chemical laws, are now laid aside, and we reason more soberly, 

 interpreting past changes in the mineral structure of the earth by 

 our experience of the laws by which the operations in the material 

 world are governed. Every accession to our knowledge of the older 

 sedimentary, highly consolidated, and semi-crystalline rocks, renders 

 the probability greater that they were formed in the same manner 

 as those now in progress of formation in existing seas ; in short, that 

 they originated from the waste of pre-existing lands. As Astronomy 

 leads us to contemplations of immensity of distance in space, thus 

 does Geology lead us to contemplate distances in past time almost 

 as boundless ; equally difficult for us to form a conception of, but, 

 although not capable of measurement, not less certain. We are 

 thus brought to admit the truth of another of the fundamental doc- 

 trines of the Huttonian theory, laid down by its author more than 

 half a century ago, and some years afterwards so eloquently illus- 

 trated by his disciple and friend Playfair, whom I am proud to call 

 my first master in Geology, " that in all the strata we discover proofs 

 of the materials having existed as elements of bodies, which must 

 have been destroyed before the formation of those of which these 

 materials now actually make a part*." We learn from Professor 

 Sedgwick, that in the north of England there are chloritic slates 

 alternating with countless contemporaneous ribs of porphyry, as well 

 as with trappean conglomerates and slaty beds, derived mechanically 

 from materials of igneous origin. M. Abich of Dorpat considers 

 that certain dark green grains disseminated through the lowest beds 

 of the Lower Silurian " Pleta," or Orthoceratite limestone of Russia, 

 are the detritus of the ancient augitic rocks of the Finnish frontierf. 

 The least fragment of an organic body in the lowest deposits, it is 

 evident, must have been encased in silt or mud, and that silt or 

 mud must have been derived from pre-existing rocks, and most pro- 

 bably rocks exposed on land to the destructive power of meteoric 

 agents. We are told by Mr. Lyell that the Potsdam sandstone, the 

 lowest of the Silurian strata of North America, at the Falls of Mont- 

 morency near Quebec, is remarkable for containing boulders of enor- 

 mous size — the largest he ever remembers to have seen, he says, in 

 any ancient stratified rock. He measured some of them, which 

 were eight feet long. They consist of the same gneiss as that on 

 which the sandstone rests. He also observed in the same sandstone, 

 on the borders of Lake Champlain, ripple- marks on the surface of 

 its flags. 



Several of the works of geologists which have been published 

 during the last year have supplied much additional evidence of 

 metamorphic action ; none more important, I may say more conclu- 

 sive, than is contained in the work of Sir R. Murchison on Russia, 



* Illustrations of the Huttonian Theory, p. 5. t Murchison's Russia, i. 28. 



