56 PKOCEEDTNGS OE THE GEOLOGICAL SOCIETr. 



the crystalline series as it emerged from beneatli theMesozoic strata. 

 Turning southward we next went by the Brunni Pass to DissentiSy 

 in the Upper Eheinthal, and thence crossed the Lepontine Alps by 

 the Lukmanier. Erom the top of this pass we crossed over into 

 the Yal Piora, thus examining again some of the work done in 

 1883, and linking it on to the present section. From Olivone, 

 which stands at the foot of the steeper part of the Lukmanier Pass, 

 we descended the Yal Blegno to Belliuzona, whence we travelled 

 to Lugano, following the crystalline schists till they disappeared 

 under Trias sic rocks on the shores of that lake. This section com- 

 pleted, we made our way to Ivrea, at the mouth of the Dora Baltea, 

 ascended that valley to Aosta, crossed the St. Bernard to Martigny, 

 and finished by examining, not for the first time, a part of the 

 northern crystalline axis together with the remarkable overlying 

 conglomerate of Carboniferous age at Yernayaz, in the Ehone Yalley. 



I have risked the charge of egotism in giving these personal 

 details for two reasons. One, because this general sketch will faci- 

 litate reference later on to the various facts which I have learnt 

 during my journeys ; the other, because I wish to show that, if I 

 express a decided opinion on any point, it has not been formed with- 

 out considerable labour and an honest endeavour to qualify myself 

 for the work. Here I may venture to repeat, with increased em- 

 phasis, the remarks which I made last year as to the importance of 

 accumulated experience in forming conclusions in regard to petrology, 

 a thing true in working at metamorphic rocks even more than 

 igneous rocks. It is often almost impossible to express in words 

 the appearances, whether under the microscope or in the field, which 

 may be absolutely convincing to an experienced worker, and which, 

 notwithstanding, even if they could be actually exhibited to an in- 

 experienced petrologist (however great his skill in other branches of 

 geology), would probably speak to him in a language which would 

 be but imperfectly understood. All departments of geology have their 

 difiiculties, but in none, I think, are they so grave as in this part of 

 petrology. Many a time have I felt tempted to despair, so vast did the 

 task appear, so hopeless the problems which it presented for solution. 

 It is very easy to strike out brilliant hypotheses if you will only 

 limit your field of study. The chemist who confines himself to his 

 laboratory, the lithologist whose eye is glued to his microscope, the 

 field-geologist who is vowed to total abstinence from that instrument, 

 in turn put us to temporary shame by the seeming clearness with 

 which they elucidate our difficulties ; but, as our experience widens, 

 the guiding star to which they so confidently pointed proves to be 

 but an ignis fatuus, and the theory which once pranked it so bravely 

 is ignominiously dismissed to the limbo of exploded hypotheses. 



Yet more, I do not believe that the study of any one district, 

 however conscientious that study may be, will suffice. Each region 

 has its peculiarities, which, while they are liable to mislead us on 

 some points, may clear up our difficulties in regard to others. Hence 

 a comparative study of several districts will often enable us to avoid 

 erroneous inductions, or to feel a confidence in our conclusions which 

 would be unattainable with a more limited experience. When a 



