Cxlvi PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



that the potash-granites arc the normal type, and that other granites 

 are formed by the addition of bases. He also points out the great 

 difficulty in deciding on the quantities of the component minerals by 

 the eye alone, and adds that, though the potash-granites of Leinster 

 arc more persistent in external character than the Newry granites, 

 the latter are quite as regular in chemical composition. 



A section of the gravel-beds at Taunton, in Somersetshire, was 

 contributed by Mr. J". Pring ; and the very last paper of our late 

 member, Mr. Joshua Trimmer, was on his favourite subject, the dis- 

 tribution of the superficial detritus which covers up most of the con- 

 solidated, and hence, in part, metamorphosed, strata of the earth. In 

 the Gorlstone cliffs of Norfolk, Mr. Trimmer recognized an upper and 

 a lower Boulder Clay; and this very fact ( proves that the old so- 

 called diluvium was the result, not of an abnormal and instantaneously 

 acting cause, but of a long- continued series of natural causes, marked 

 in this case by the recurrence of glacial phenomena at two successive 

 periods. Mr. Trimmer considered this portion of the earth to have 

 been gradually sinking at the time, and to have been thus subjected 

 to the overflowing of the northern wave, carrying with it fields of 

 boulder-charged ice. 



Having thus incidentally referred to the preceding minor papers, 

 I shall close this notice of papers on Descriptive Geology by a brief 

 commentary on the two papers which Sir R. Murchison has read 

 before the Society during the present session. Nothing can be 

 more gratifying to us, or more encouraging to our younger mem- 

 bers, than to observe the undiminished energy with which Sir Ro- 

 derick strives to put the last finishing touch to his labours on the 

 rich subject of Silurian deposits. The first of the two papers was a 

 supplementary comparison of the Silurian rocks and fossils of Nor- 

 way as described by M. Theodor Kjerulf, with those of the Baltic 

 provinces of Russia as described by Professor Schmidt, and both 

 with their British equivalents. In South Norway there is a vast 

 development of unfossiliferous rocks, which, as in our own country, 

 are denominated Cambrian ; but we may at least hope that hereafter, 

 even in these unpromising rocks, the same success will attend the 

 searchers for fossils as has already rewarded our British inquirers, 

 and that it will be ascertained without doubt whether any epoch 

 antecedent to that of Siluria was marked by organic life. The recent 

 discovery, by Mr. William Rogers, of the genus Paradoxides in the 

 metamorphic rocks (ordinary mica-slate) of the neighbourhood of 

 Boston, United States, is one additional proof that we ought not to 

 despair of making many similar discoveries, some, as in that case, 

 within the Silurian epoch, and others probably far antecedent to it. 

 M. Kjerulf divides the Silurian system of Norway into three groups 

 distinguished by their physical characters, or, in other words, by the 

 conditions under which the several deposits had been formed : and 

 these he names from the localities where they can be best studied, 

 the Oslo, the Oscarskal, and the Malmo or upper group ; and then 

 further establishes fourteen subdivisions. 

 The sandstone and conglomerate at the base of the Oslo group is 



