122 Horner's Geological Address. 



morphic" to this peculiar altered structure of sedimentary 

 rocks, — a term which has been since universally adopted ; 

 and every year has disclosed new facts from all parts of the 

 world, in confirmation of the theory that the older crystal- 

 line and indurated schists, limestones, dolomites, and quartz- 

 ites, and many similar beds of more modern date, were not 

 deposited with a structure such as they now present, but 

 were accumulations of detrital matter, transformed into their 

 present condition mainly by the action of heat, accompanied 

 by other chemical action, and the powerful agency of steam 

 and elastic forces under enormous pressure. A very inge- 

 nious process, invented by Mr Brockedon, described in a 

 short paper read before us last year, by which he converts, 

 under very powerful pressure, the powder of graphite into a 

 solid mass, having a conchoidal fracture, and undistinguish- 

 able from the most compact native black-lead, shews that 

 pressure alone may convert fine detrital matter into solid 

 stone. 



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 un- 

 supported 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 ex- 

 perience 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-crystal- 

 line rocks, renders the probability greater that they were 

 formed in the same manner as those now in progress of for- 

 mation 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 doctrines of the Huttonian theory, laid down by 

 its author more than half a century ago, and some years af- 



