J. E. Marr — Cambrian and Silurian Rochs. 245 



layer, it must force up raountain chains along lines of least 

 resistance. The sustained pressure would continually keep fresh 

 layers of the solid interior or of its own material at the liquefj'ing 

 point, and press them out in turn — imperceptibly deepening the 

 ocean basins where they are deepest and raising the shallower 

 parts to higher levels, thereby slowly lessening the surface area 

 of seas. On the other hand, the dry land would extend in a 

 corresponding degree, and its surface become more diversified, for 

 new mountain chains would perhaps in succeeding ages have a 

 tendency to reach greater elevations. Geologj'^ itself supports this 

 hypothesis. The records of the PalEeozoic rocks point to a com- 

 parative uniformity in the earth's surface in remote times, there 

 being neither evidence of great depths in the sea, nor of mountainous 

 elevations in the land, and palgeontological evidence shows these con- 

 ditions to have been progressively modified until the present day. 

 If mountain chains and volcanic outbursts were caused only by the 

 cooling of the earth, we should find, instead of the uniformly 

 shallow sea of the older Paleeozoic rocks — and the almost uniformly 

 level land of the Carboniferous — evidence of even greater inequalities 

 of surface than now exist. 



While therefore upon this theory the greatest depths of the ocean 

 may always have been permanent, the banks and ridges of less 

 depth with islands occasionally rising to the surface, and crossing 

 the Atlantic and Pacific, must either be rising or sinking. If they 

 do not mean changes of level in the sea-bottom, whether of past or 

 present elevation, what do they mean ? Forces are unceasingly 

 acting, and there is no reason why an elevating force once set in 

 action in the centre of an ocean should cease to act until a continent 

 is formed. They have acted and lifted out from the sea, in com- 

 paratively recent geological time, the loftiest mountains on earth. 

 Mr. Wallace himself admits repeatedly that sea-beds have been 

 elevated 1000 fathoms, and islands have risen up from depths of 

 3000 fathoms ; and to suppose that the upheaving forces are limited 

 in power is, it seems to me, to again quote from Island Life, "utterly 

 gratuitous, and entirely opposed to all the evidences at our com- 

 mand." 



In conclusion, I will only add that these ideas are obviously put 

 forward tentatively, and await further proof or disproof. I propose 

 next month to make the subject clearer by means of a diagram. 



II. — The Classification of the Cambrian and Silurian Eocks. 

 By J. E. Makr, B.A., F.G.S. 



A PAPER by M. Barrande, which has been recently published,^ 

 seems to call for some reply. M. Barrande, whilst working 

 out the succession in Bohemia, adopted Sir R. I. Murchison's name 

 " Silurian," and even applied it to lower rocks than did ever 



^ " Du Maintien de la Nomenclature etablie par M. Murcliison, par M. J. 

 Barraude," Extrait du Compte Keudii Stenograpliique du Congres luternational de 

 Geologie, tenu a Paris du 29 au 31 aout et du 2 au 4 Septembre, 1878. 



