NATURE 



[May 30, 1872 



subject for examination arc recommended to read that part 

 of Koscoe's " Lessons in Elementary Chemistry " which 

 treats of Inorganic Chemistry (pp. 1-268, new edition, 

 I S69). The practical examination will be in the follow- 

 ing subjects as treated of in Harcourt and Madan's 

 " JCxercisesin Practical Chemistry" :— i. The preparation 

 and examination of gases (pp. 59-107) ; 2. The qualita- 

 tive analysis of single substances (pp. 247-300 ; see also 

 sections IV. and V., omitting that which relates to sub- 

 stances or properties of substances not referred to in the 

 Analytical Course). (4.) The Elements of Physics. 

 Candidates offering themselves for examination in this 

 subject "ill be expected to show an acquaintance with 

 Part I., together with any two of Parts II., III., IV. of the 

 following treatise ; — " Pllementary Treatise on Natural 

 Philosophy," by Ueschanel. Translated and edited by 

 Prof. Everett. Part I. Mechanics, Hydrostatics, and 

 Pneumatics. Part II. Heat. Part III. Electricity and 

 Magnetism, of which chapter 39 may be omitted. 

 Part IV. Light and Sound (which will be published in a 

 few weeks(. 



THE MURCIIISON CHAIR OF GEOLOGY 



UPWARDS of a year ago we duly chronicled the 

 founding of a chair of geology and mineralogy in 

 the University of Edinbuigh by Sir Roderick Murchison, 

 and we augured that the munificence of the founder would 

 not be long in bearing fruit. It is pleasant to learn that 

 the first session has been concluded successfully, and that 

 the class has been greatly larger than the most sanguine 

 friends of geology m Scotland had anticipated. In ad- 

 dition to the ordinary lectures of the class-room, there have 

 been frequent afternoon excursions to the field, where the 

 piinciplesof the science have been learnt in a way in 

 which they cannot be from mere lectures or books. 

 Edinburgh is peculiarly favoured by nature for instruction 

 of this practical kind. The crags and ravines whicli 

 surround, or even stand in the midst of, the streets and 

 gardens furnish admirable models of many of the more 

 important and striking facts of physical geology. These 

 advantages have been fully made use of during the past 

 winter and spring. There has been, we are told, a brisk 

 sale of geological hammers, and bands of hammerers have 

 been seen on Saturday afternoons wandering over hill- 

 side and quarry. At the close of the session Prof. Geikie 

 and his students celebrated the termination of their 

 labours together by a week's holiday in the island of 

 Arran. For such an excursion good weather is the first 

 grand essential, and in this respect the party appears to 

 have been singul.-^ily lucky. The days were bright and 

 bracing, so that from the highest hill tops the eye could 

 ■w-ander over all the wide expanse of fitth and fell which 

 lies between the mountains of Jura and the far-off faintly- 

 seen uplands of Galloway. 



It was chitfly to the northern half of the island that 

 the attention of the excursionists was devoted. They 

 traced, of course, the well-known and often-described 

 features — the granite mountains and veins, the schists, 

 the liap-dykes, the carboniferous sandstones, con- 

 glomerates, limestones and tuffs, the raised beaches, &c. 

 But they noted some points which deserve, perhaps, more 

 special remark than has yet been accorded to them, and 

 of these we have been furnished with the following 

 jottings : — 



I. Some interesting observations were made on the re- 

 lation between the joints of the granite and the forms of 

 surface into which that rock has been wasted. Every- 

 body who has seen the Arran mountains remembers their 

 sharp serrated ridges and deep corries. It was noticed 

 in p.Il the examples which were visited that each knife- 

 edged crest coincided with the intersection of two sets 

 of joints dipping in opposite directions, as the ridge of a 

 roof coincides with the line along which the two opposite 



slopes meet. Where the one set of joints differed most 

 in angle of inclination from the other, there was seen to 

 be a corresponding difference in the slope on two sides of 

 the crest, the highly inclined joints having .1 steep face, 

 sometimes quite a precipice, on their side, while the less 

 inclined joints had a gentler declivity on the other. From 

 the summits it seemed as if the changes in the direction 

 and inclination of the granite ridges were largely due to 

 changes in the trend and slope of the systems of cross- 

 joints. But there was not time to work out this problem. 



2. Some mineralogical and petrographical facts of in- 

 terest were gleaned. The passage of the Arran pitchstone 

 was traced into a dull pearlstonc which appeared to be 

 closely connected with, if, indeed, it did not pass into one 

 of the pale compact felstones or " compact felspars." The 

 common association of pitchstone with the tertiary vol- 

 canic rocks of the west coast, and its entire absence from 

 any rf the abundant palx-ozoicvolcanic masses of the main- 

 land, raises thesuspicionthat perhaps theArran pitchstones 

 are likewise of tertiary date. The association of these 

 pitchstones with some of the characteristic felstones or 

 porphyries of that island also suggests as late an origin 

 for the latter. Some facts, indeed, were noted, which, if 

 properly worked out, might throw light on this question. 

 It was observed, for example, that in the picturesque 

 columnar ridge above Corriegills the columns are so 

 arranged as to indicate that the mass of rock llowed along 

 and consolidated in a trough or hollow. Was this hollow 

 a valley carved out of the denuded surface of the car- 

 boniferous rocks, and did the porphyry flow into it as a 

 couli'c? A phenomenon of rare occurrence was noted in this 

 Corriegills porphyry. Usually the quartz in such rocks 

 exisis merely as irregularly-shaped blebs or grains. In 

 this rock, however, it is crystallised, and frequently ap- 

 pears in little doubly-terminated pyramids. Some of the 

 party spent half an hour in gathering up perfect crystals 

 from the weathered hollow^s of the rock. These crystals 

 do not occur in amygdaloidal cavities but as essential 

 constituents of the rock. In the Goatfell granite some 

 cavities were found with well crystallised quartz, and one 

 of the party was fortunate enough to light upon one 

 cavity from which he obtained a handful of small cairn- 

 gorms. 



3. The moraines of the Glen Cloy afforded a pleasant 

 afternoon. It was matter for surprise to some of the 

 party that amid all that has been written about Arran 

 these tiuly remarkable moraines have not received more 

 notice. It is true, they do not lie among the group of the 

 higher mountains of the island, and they have not the 

 magnificent setting around them which they would have 

 had if they had stood in Glen Rosa, or Glen Sannox, or 

 Glen lorsa. But in none of these glens, even though 

 they plunge into the very heart of the central mass of 

 granite, is there anything in the way of moraines at all to 

 compare with the huge concentric mounds of rock-rubbish, 

 cumbered with blocks, which roughen the bottom and 

 sides of the deep recess in which the upper part of Glen 

 Cloy terminates. The plateau which served as the snow- 

 field whence the Glen Cloy glacier was fed rises to an 

 average height of only about 1,400 or 1,500 feet above the 

 sea, while the neighbouring granite peaks are about twice 

 as high. Yet the higher granite mountains have afforded 

 comparatively few and small moraines. It gives a good 

 notion of the severity of the climate during the glacial 

 period to reflect that the little isolated patch of elevated 

 ground, forming now the island of Arran, was large 

 enough to nourish, even on its lower plateaux, snow-fields 

 and glaciers. 



4. Many striking lessons were learnt regarding some of 

 the broad aspects of atmospheric denudation. Particu- 

 larly v.-cre these lessons brought home to the mind among 

 the wasted crags and corries of the gr.anite mountains. 

 Granite which, in the popular cieed, is regarded as one of 

 the most imperishable of rocks, was seen to be covered 



