ANNIVERSARY ADDRESS OF THE PRESIDENT. CXXV 



or vitreous structure ; sometimes a complete solution, probably partly 

 due to the water combined with the rock. 



I hope that what I have said will give a fair idea of the sys- 

 tematic and able manner in which M. Delesse has treated his sub- 

 ject advancing step by step from the simple to the compound, the 

 laboratory of the chemist leading to Nature's present laboratory the 

 volcano, and that again to the more recondite sources of meta- 

 morphism, viz. trap-rocks ; but, as to follow him through the latter 

 would require an inordinate space, I must merely content myself 

 by observing that the same order is observed, and that every step of 

 the investigation is illustrated by numerous examples, either based 

 on the observations of others, or on his own, as well as by the che- 

 mical analysis of many of the products of metamorphism, — whilst the 

 results are striking proofs of the value of M. Delesse's inquiries, and 

 of the ability with which he has pursued them. In respect to com- 

 bustible substances, he deduces from his inquiries that they appear 

 under four aspects, corresponding to the different degrees of normal or 

 general metamorphism, namely graphite, anthracite, coal, and lignite, 

 and then illustrates the action of the trap-rocks upon each. New Cum- 

 nock in Scotland has afforded many illustrative specimens, originally 

 collected by M. Boue, but analysed by M. Delesse, though here it is 

 rightly assumed that the coal has passed through the several stages of 

 metamorphism up to anthracite, and finally graphite, through the action 

 of the trap, having become impregnated in the course of the change 

 with a large amount of mineral matter. The lignite of Omenak in 

 Greenland, collected during the recent voyage made by Prince Na- 

 poleon, and, where in contact with the trap, metamorphosed into an- 

 thracite, exhibits even more striking results, as by analysis it is found 

 to consist of carbon 50-64, water and traces of bitumen 15-60, car- 

 bonate of lime 18-43, of magnesia 6*27, of iron 2-03, alumina 7-08; 

 the anthracite having become useless as a combustible, being 

 highly impregnated with mineral matter, sometimes in the form of 

 veins. Wiiilst, however, these are the effects of contact with trap- 

 rocks, M. Delesse points out, from various examples, that coal and 

 anthracite, when imbedded in the trap, may have escaped such 

 external metamorphism, — as an illustration of which, he cites the 

 combustible, apparently a lignite, of Dellys in Algeria, observed by 

 M. Ville, which, though imbedded in trap, has not passed into the 

 state even of charcoal or of coke, as it would have done in contact 

 with lava ; but has been simply changed into a dry coal, which under 

 distillation yields bituminous and ammoniacal matter. 



M. Delesse deduces from this partial change a reason for con- 

 sidering the heat comparatively feeble ; but I am more disposed to 

 ascribe the differences of result to the more or less porous character 

 of the enveloping trap, and the consequent greater or less facility with 

 which the volatile ingredients might have escaped from the combusti- 

 bles, although it is very possible that the heat in this case may not 

 have been very excessive ; and the impregnation with mineral matter 

 indicates, as in other cases, that the metamorphism is due in part 

 to other causes, and not to heat alone. The change produced is, 



