John MacCulloch

“ It is so great an advantage to possess one term well understood, and understood as the language of philosophy should be, in all countries, that we can scarcely find a motive sufficiently powerful to induce us to change this received name. Under these circumstances we have every reason to retain the term graywacke, however jarring to English ears, and it is the excess of fastidiousness to reject on account of its sound, one word from such a polyglot of unmelodious and ill compounded Greek, French, and German terms, as assail the mineralogist on every side. ”

“ The late introduction of a new chemical nomenclature, has possibly, in conjunction with other causes, excited a taste for neology, which it behoves us to restrain by every method in our power, and it is the duty of our Society to watch over and protect the science from those changes which will, if not restrained, shortly inundate us with as many names as we have writers. ”

“ In matters of terminology I have felt an inconvenience not peculiar to myself, which I have been unable to remedy without appearing to attack hypotheses that I would willingly have let alone, as the language of controversy is unpleasing, and appears rather calculated to retard than promote the progress of an infant science ”

“ If the unnecessary multiplication of distinctions and names in mineralogical nomenclature is productive of toil by introducing a cumbrous apparatus into the science, it has at least the merit of conducing to accuracy of description. That is a much worse extreme, which by rejecting all such distinctions confounds together under one sweeping term, all sorts of substances, which, however differing in individual character and however constant and uniform in the character each severally assumes, are associated by only one common circumstance, the accidental one of position. ”

“ To a mere observer, uninfluenced by systems, it exhibits the remains of a disposition originally stratified and horizontal, but disturbed, inclined, and broken, by subsequent changes;—a disposition, which however uniform in more distant times, has been altered to its present one with a partial, not a total loss of its original character, by revolutions of which the antiquity and magnitude are unknown to us, and by agencies which we are ill able to explain. ”

“ My wish is rather to excite the industry of those who cultivate geology, to the investigation of the still recondite chemical actions, from which alone we can hope for the solution of these and numerous other difficulties which attend us. ”

“ My design is merely to suggest the necessity of considering the greatness of the scale on which Nature operates, and the probable occurrence of a chemical texture, if I may use such an expression, different from, and additional to that which may be observed in the smaller masses, and probably as constant in the larger masses which constitute the different rocks, as the minuter crystallization is in the smaller parts which unite to form them. ”

“ We have here an example of the columnar form existing in a very perfect manner in a rock, which however it may bear a considerable analogy to greenstone, and through that to those rocks which more commonly exhibit the columnar shape, is still sufficiently distinguished from them all by the great predominance of the felspar. There is no difficulty in conceiving that the same causes presided at the formation of both, when we consider the similarity of geological structure and position which pervades all the rocks distributed under the heads of basalt, greenstone, and syenite. ”

“ We have long been indebted to foreign countries for substances which our own island produces in abundance, and in no instance have the powers of established habits and prejudices been carried further than in the preference given to many of their insignificant marbles and porphyries, while our own, either similar or superior, have been neglected. To encourage commerce and the arts is not unworthy of a Society, which, like ours, has in view among other objects, the investigation of an important branch of the natural history of our own country. ”

“ Nor is the great lamellar texture which has so often been considered as the effect of stratification, peculiar to granite. In examining the Cuchullin hills in Sky, I have observed that the syenite and greenstone are bedded as it were in layers, either curved or straight, either horizontal or slightly inclined, resembling so much the disposition of granite beds, that even an experienced eye would at a distance be deceived by them. It is not necessary to illustrate this view by any further analogies, as every person's memory will afford examples in the disposition of some kinds of porphyry. ”

“ Almost every where it is disturbed and contorted to a great degree. The beds are easily traced in several places, where quarries have been dug, or mines wrought; and in many others the inclination of the soil and the action of water, have laid the edges bare for some hundreds of yards together. The perfect similarity of its disposition to that of the limestone which accompanies clay slate all over the Highlands of Scotland, and more particularly to that of the island of Lismore, would suffice to determine its true character, even without the detail of specimens. ”

“ All these beds are traversed by numerous veins of quartz, and they alternate with each other without any regular order, the beds not forming a series passing from the coarse to the fine grained, but a fine clay slate often following close upon a coarse graywacke, and being succeeded by a similar rock. Here then we have an instance of a fact, of which the observations of every geologist will furnish many other examples, namely, the occurrence of clay slate among those rocks called rocks of transition, their alternation rendering this part of the fact indisputable. ”

“ I cannot however dismiss this subject of Rona without pointing out to future observers the singular contortions exhibited as well by the gneiss as by the hornblende rock where they come into contact. I may also venture to suggest that the rock of Blue Bay, described as a mixture of hornstone, chalcedony and quartz, appears to be a modification of gneiss, exceedingly intersected by veins of quartz and felspar, and probably of granite. It exhibits no genuine hornstone; that part of it which has at first sight this appearance, being an intimate mixture of quartz and felspar. ”

“ For, the hornstone, the claystone, the trap and the felspar, which constitute the bases of these several rocks, although often containing crystals of felspar, are yet perhaps as frequently destitute of that accidental substance. I am not an advocate for increasing words, and encumbering our language with unnecessary terms, but that confusion which arises from applying one term to many substances, is at least as faulty and a greater cause of error than the accumulation of an unweildy stock of synonymous ones. ”

“ The mica slate is often remarkable for containing numerous and very large cubical crystals of pyrites, an occurrence much less frequent in this rock than in clay slate.
Veins of quartz traverse it in innumerable places, and it is also interspersed with compressed nodules of quartz, which bear no marks of attrition, but are intimately united to the mica slate, or chlorite slate, in which they occur. They are frequently characterized by a beautiful transparent brown colour, which renders them objects of much research and high price among lapidaries. ”

“ The accompanying specimens will preclude the necessity of describing a rock of no uncommon occurrence, whether the name by which I have designated it be one about which mineralogists are agreed, or not. It has unfortunately been applied to so many different stones, that it is utterly impossible to steer clear of difficulties. Among the reforms of nomenclature, in the departments of rocks, the term hornstone, and the various substances which have been classed under it, call loudly for examination. ”

“ In the present state of geological science, it would appear a safer practice in this case, as in many others, to describe that which actually exists, without the use of hypothetical terms, which only serve to perplex the observer, and to mislead the student, who either boldly pronounces on the character which suits his particular creed, or modestly supposes himself incapable of sound observation, because he is unable to see that which is not visible. ”

“ When the condition of the stone is of that intermediate nature which renders its precise place uncertain, the modified term of syenitic greenstone is easily applied. In difficult cases where these rocks are still more varied in their composition, and in all others where a multiplication of terms would lead to an unbounded and unnecessary nomenclature, it will even be preferable to distinguish the variation from the more rigid form by a detailed description rather than to encumber the science with a useless neology. ”

“ It is therefore evident, that no general force acting on a large mass has been the cause of these curvatures, but that they have been produced by the application of numerous partial forces acting on different parts, and capable of stretching those sets of laminæ on which the forces have acted, independently of the neighbouring ones. It is equally evident, that a mere state of softness in the stratum of schist is insufficient to account for this partial and complicated effect, but that it must have taken place when the rock was in a state of tenacious fluidity. ”

“ Such rocks are not of uncommon occurrence, nor is it uncommon to meet a rock in which quartz, felspar and mica are so compounded, as to form a true granite with crystals of hornblende superadded to the compound. Great confusion must follow the separation of these from the granites, and their union to the syenites above described. Their structure and characters are in all cases granitic, nor does the eye readily detect the difference till the darker parts are minutely examined, when the crystals of hornblende may, and that often only with much care, be distinguished from the mica. ”

“ Those who have been engaged in similar observations on an extensive tract of country, well know how difficult it is to fill up all the chasms which the nature of the ground forms in the pursuit of a series of rocks. Yet I have very little doubt that a true gradation exists here, between mica slate and graywacke slate, and that the usual intermediate member, primitive clay slate, does not occur as a necessary part of the series, but that it is irregularly alternated with the graywacke. ”

“ I hold it necessary however that the word syenite, if it is to be used as a generic term, should be limited, as rigidly as the ever varying and mingling composition of rocks will admit, to those compound rocks which are akin to greenstone in their chemical and essential characters, or consist of certain notable and distinct proportions of felspar and hornblende, but in which the felspar is either the predominating ingredient, or is crystallized in masses so large and distinct as to remove the compound from those similar compositions now generally known by the name of greenstone. ”

“ Let us not suffer ourselves to be misled by the imposing aspect of independence and disinterestedness which philosophy assumes when employed in investigating general principles, and, contented with the splendour by which science is surrounded, refer to others the humble task of converting it to useful purposes. ”

“ If the quartz rock of this tract be a primitive rock, then the limestone is necessarily a primitive rock also, notwithstanding its bituminous nature, and accurately stratified structure, since it alternates with it. But, if this rock is not a primitive, but a transition rock, then the limestone also must be removed from the first class of rocks to the second. ”

“ I may remark, that the junction of these different rocks does not appear to be attended with any change in the nature of either. In one of the veins there is a portion containing a compound of an uncommon nature, but somewhat resembling the rock above described, being a mixed mass of crystals of augite, hornblende, and felspar. Loose specimens of black pitch-stone are also found on the beach, arising in all probability from some vein of that substance. But the production for which it is most remarkable is the green chalcedony, or heliotrope as it is generally called. ”

“ There is no further difficulty in conceiving that a rock may constitute a huge bed separable into horizontal laminæ as regular as the strata of a mechanical deposit, than in conceiving that the island of Staffa is separable into columnar fragments, or the rock of Devar into vertical laminæ. It is true that we have not yet produced any instance of continuous, horizontal laminar concretions, which are incontrovertibly not mechanical, yet its existence implies no chemical impossibility. That which occurs on a small scale may occur on a large. ”

“ It is not one of its least advantages that it forms a school of practical knowledge for those whose opportunities are circumscribed by the scarcity of scientific institutions or schools of this nature, and with this view, even the humble offering of a new habitat is deserving of record. ”

“ The specimens of it seen here, occur in a vein of quartz, which traverses a talcy clay slate, a slate accompanied by a singular rock, which I will also describe. It only offers the common aspect of this mineral, which hitherto has exhibited no remarkable varieties, and is of a very decided character. The crystals of disthène occur in the quartz vein, as well as in the clay slate which bounds it, and pass indifferently through both, without any change of their direction or appearance, marking clearly a common condition in the schist and the quartz, at the period of their formation. ”