190 Anali/sis of Scientific Books. 



Ivy-bridge, at the base of the granitic mountain called Three 

 Barrow-Tor. In Mount St. Michael in Cornwall, a white gra- 

 nite penetrates a schistous rock ; and in both situations, as at 

 Tor-nid-neon, the granite of the veins is quite continuous with 

 that of the mass, and increases in the sraaliness of its crystals 

 with the contraction of the veins. Mr. Jameson himself has 

 described some in his work on the mineralogy of Scotland. 

 M. de Saussure saw such veins at the Valorsine and Lyons, on 

 the banks of the Saone ; and gave a detailed description of 

 them in the twelfth chapter of the second part of his For/ages 

 dans les Alpcs, Vol. I. p. 530. Lastly, the German minera- 

 logist, Lasius, describes some veins of granite of Reh-berge- 

 Klippe, on the confines of the granitic group, which forms the 

 centre of the Hartz mountains *. 



So many analogous observations, made in countries so far 

 asunder, lead us to bestow on a phenomenon, whose generality 

 appears to be proved, more importance than we would have 

 allowed, had it been only once presented as a single exception 

 to a general rule. 



Mr. Necker draws the following conclusions. 1st. Granite 

 is not in all cases, as has been for a long time believed, the 

 most ancient of rocks. This fact has been lately placed beyond 

 all doubt, by Mr. Von Buch's observations in Norway. He 

 found beds of granite incumbent on micaceous schist, ar- 

 gillaceous schist, and gabro. He has observed also a granite 

 of transition alternating with the greywacke and transition lime- 

 stone t. 2d. The most important deduction is, that there may 

 be, and actually exist, cases where the lowest rock in the order 

 of super{)osition, may not be the oldest ; and where, conse- 

 quently, the principle on which are founded all the systems of 

 geognosy, and which have been hitherto regarded as an axiom, 

 would lead us into serious errors. It is therefore important, 

 that geological observers should direct their researches towards 

 the points where two rocks of a different nature meet ; the junc- 

 tions, often difficult to discover, almost always concealed by 

 debris, vegetation, or the beds of rivers, are nevertheless, in 

 many instances, the places where we may hope to discover the 

 secrets of nature ; the spot where we shall find the true data for 

 judging of the mutual relations of rocks. The stratiform or schist- 

 ous rocks, whose beds and/o/ta give us evidently the idea of slow 

 and successive deposites, are seldom separated bluntly from 

 each other ; the passage of one rock to another is generally 

 gradual and imperceptible. It is not so with rocks such as the 

 granites of plains, syenites, porphyries, which occur in irre- 

 gular masses, without vestiges of beds or folia, and which 



* Berhachtun^ Tiber die Harlz-geberge, Vol- !■ p. 94. 

 t Voi/age en Norwegt et en Laponie. 



