156 Henry Hicks — On the Northern Palceozoic Rocks. 



riG.4. The same. Eight valve, with numerous colour bands, and exhibiting the 

 posterior ear. 



„ 5. The same. Right valve, with the posterior ear. 



,, 6. The same. Eight valve, ears not shown. 



„ 7. Aviculopecten papyraceus, Sow. A nearly complete left valve with portion of 

 the right. Shale 2| feet over Calderwood Cement Stone, L. Garb. Lime- 

 stone Group, Gleibe Quarry, E. Kilbride. Cabinet of Mr. A. Patton, 

 E. KUbride. 



„ 8. BelleropJion dectissatus, Fleming, with its greatly thickened and reflected lip 

 with the lateral expansions over the umbilicus. Linn Quarry, near Dun- 

 fermline, Fife ; shale connected with one of the L. Limestones (L. Carb. 

 Limestone Group), K'at. size. 



,, 9. and 10. B. deciissatiis, Flem., var. undatus, E. Etheridge, jun. Woodhall, 

 Water of Leith, near Edinburgh, in shale of the Wardie Shale Group, Lower 

 Carboniferous or Calciferous Sandstone Series. (The specimens from this 

 bed are usually crushed.) 



III. — Some Considerations on the Probable Conditions under 



WHICH the PALiEOZOIC EOCKS WERE DEPOSITED OVER THE 



Northern Hemisphere. 



By Henry Hicks, F.G.S. 

 {With a Folding Table.) 



THE numerous excellent observations whicli have been made 

 in recent years relative to tlie Palaeozoic rocks in different 

 countries in the Northern Hemisphere, require that we should now 

 and again attempt to summarize the results obtained, and by that 

 means bring before the mind more clearly any advance in our 

 knowledge of past changes which has been made, as well as note 

 those blanks which are still left for future investigations. In these 

 considerations I cannot attempt to treat fully the various observa- 

 tions made, but I will endeavour to notice the chief results, or those 

 points upon which new light seems to have been thrown. 



Cambrian and Loiver Silurian. — Paleeozoic time is considered to 

 have commenced in Europe with the deposition of the earliest Cam- 

 brian rocks, and in America, by most authorities, with the Huronian 

 rocks. To endeavour to trace out the conditions of the Northern 

 Hemisphere at that early period has been one of the most important 

 subjects which geologists have attempted to unravel in recent years. 

 The researches which have been made prove conclusively that in 

 America, before the Huronian rocks were deposited, a continent of 

 great extent existed there. It is evident that in Europe at this time 

 there was also a continent of large size, as portions of it are now 

 visible in Spain, Bohemia, France, England (Malvern^ and St. 

 David's), 2 Scotland, Norway, the Loffoden Islands,^ etc. From the 

 Table it will be seen that the rocks forming this old Pre-Cambrian 

 land consist chiefly of gneiss, or granite, but there are also in some 

 places beds of limestone of considerable thickness. All the rocks 

 are found to be in a metamorphosed state, and the bedding uncon- 

 formable to those overlying them. On both sides of the Atlantic, 

 they are to be seen at various places from the latitude of 30"^ to the 

 Arctic regions, and it seems reasonable to suppose that these por- 



1 Dr. Holl, Quart. Journ. Geol. Soc, vol. xxi. 



2 Harkness and Hicks, Quart. Journ. Geol. Soc, vol. xxvii. 



3 Carl Pettersen, Geol. Mag., Sept. 1875. 



