ANNIVERSARY ADDRESS OF THE PRESIDENT. 



liii 



subjected to friction long continued or many times repeated. The 

 mass moreover of fragmentary matter usually included between the 

 opposite walls of such rents is partly reduced to fine clay or dust, 

 and partly filled with stones which have been superficially scored in 

 various directions. 



The minute study of the structure and organic contents of strata 

 of various ages, has made us of late years more and more familiar with 

 the hypothesis of a slow sinking of the ancient floor of the ocean 

 going on while it was receiving repeated accessions of sediment. We 

 must not forget that in all such cases a solid foundation of subjacent 

 rock of unknown depth, and perhaps much older than the newly su- 

 perimposed deposit, is undergoing simultaneously a change of posi- 

 tion, and that rocks still lower are undergoing, whether by cooling 

 or crystallizing, a change of structure. These very gradual movements 

 are quite as remarkable in the palaeozoic as in the tertiary periods. 

 By consulting the * Memoirs of the Geological Survey of Great Bri- 

 tain,' you will learn that in "Wales, and the contiguous parts of En- 

 gland, a maximum thickness of 32,000 feet (more than six miles), of 

 carboniferous, Devonian and Silurian beds, has been measured, the 

 whole formed whilst the bed of the sea was continuously and tranquilly 

 subsiding. In illustration of a movement of the same kind, I need 

 scarcely remind you of the coal-measures of South Wales, with their 

 numerous under-clays, each containing Stigmaria, a pheenomenon to 

 which Mr. Logan first drew our attention. Mr. Binney of Manchester 

 has since proved to us that all these Stigmarise, found in the floor of 

 every coal-seam, are the roots in situ of fossil trees, chiefly of the ge- 

 nus Sigillaria, and that they are occasionally attached to their stems 

 or trunks, — a conclusion fully confirmed by the more recent observa- 

 tions of Mr. Kichard Brown on the coal-fields of Nova Scotia. Sir 

 Henry De la Beche also, in his paper on the rocks of South Wales 

 and the South-west of England, confirms these statements, and shows 

 that subsidences of vast amount took place slowly during the accumu- 

 lation of the palaeozoic strata, the sea all the while remaining shallow, 

 in spite of a depression of one or two miles. Still later. Professor 

 John Phillips, in the second volume of the same * Survey,' has pointed 

 out analogous phsenomena in the old red sandstone of the Forest of 

 Dean ; and these strata, 7000 feet thick, are described as having been 

 formed in a sea of moderate depth. Fossil corals and shells imbedded 



