Group of Basaltic Columns

Illustration of a fragment of a basaltic column, with rounded edges, observed near Belfast, and of a group of three basaltic columns.

Inscribed in Image

  • Caption outside of boundaries of image – Group of Basaltic Columns
    London. Published by Henry Colburn Conduit Street 1816
  • Text within boundaries of image – Fig.1. / Fig. 2.

Image Details

Genre Scientific or Technical illustration
Technique Aquatints
Subject(s) Nature
Geographical Location
  • Belfast - Town or city
  • Antrim - County
  • Ulster - Province
Keywords(s) Rock formations
Colour Monochrome
Dimensions 15.5 cm x 19.8 cm
Published / created 1816

Bibliographical Details

Travel Account Narrative of a Residence in Ireland
Print or manuscript Print
Location of image in copy opp. p. 145
Alternative source

This is a link to a digital copy hosted by an external website.
Rights Courtesy of the National Library of Ireland

Related text from travel account

Where basalt does not divide itself precisely after the manner of prismatic columns, or evince a tendency to that figure on a great and general scale, it // often forms laminated spheroidal bodies, which varying in their diameters, constitute, by aggregation, rocks of considerable magnitude. The latter circumstance, in addition to the occurrence of basaltic fragments, in which a sphere appears to be enveloped by a polyhedral figure, suggested the hint for an opinion which I have been led to adopt—that a compressible laminated sphere is the primitive figure of each prismatic articulation, composing a column of basalt: and that the lateral plane surfaces, as well as the corresponding concavity and convexity of the horizontal surfaces, the trihedral processes of the lateral edges, and the corresponding truncations of the superimposed joint, result from the assemblage of spheres, under the influence of gravitation, while the component particles are in a yielding state; their laminated structure being a mechanical accommodation to the filling of those interstitial spaces, which must result from an aggregation of spheres. These ideas may be in some degree elucidated by the annexed Plate, in which the first figure exhibits a basaltic fragment from the vicinity of Belfast, where the sphere is developed by a partial decomposition of the prism; while the group shows the prevailing character of basaltic columns in general, two of the constituent prisms being detached, to show the alternate concavity and convexity of the horizontal surfaces, with the angular processes and truncations of their edges. My view of this phenomenon is not widely different from that of Monsieur Allau, which having previously appeared in the Journal de Physique, was published, as a translation, in the 23d volume of Nicholson's Journal. In concluding a paper on the contraction of artificial sandstones by fire, the natural division of basalt is alluded to, without any decided reference to the influence of fire or water; conceiving "that cracks will determine spheres of attraction, round which the particles will agglomerate; and the centres will be so much the more numerous, and the radii less as the attractive force is more considerable." But according to the idea which has occurred to me, it is the central attraction of individual nuclei, which determines the number and figure of the cracks or fissures; or in other words, that laminated spheres of basalt chemically formed by the attractive power of its constituent particles, are mechanically altered by juxta-position under the same influence. // Mr. Gregory Watt by his excellent paper in the Philosophical Transactions appears to have adopted an opinion that a spheroidal figure is concerned in the determination of the basaltic column. But I am not aware that any theory has been suggested similar to that which is here attempted. Where rocks of basalt, as is well instanced at Port Coane on the coast of Antrim, exhibit simply a spheroidal structure, it appears possible that the phaenomenon may have depended upon an imperfect process of crystallization; an inference deducible from the uneven distribution of the constituent particles; and, perhaps, also from consideration of the physical qualities of those which are predominant. For example, where alumine prevails, it does not seem impossible that this earth may influence a rapid crystallization. However, it is needless to observe that the characteristic figure of all solids is often either indeterminate, or mutilated, as the disposition of their parts to geometrical arrangement has been opposed or unfavoured by adventitious causes. Those spheres of basalt, which constitute rock-masses, clearly exhibit numerous concentric laminae, after the manner of a coated bulb: hence, in the north of Ireland, they are vulgarly known as Onion-stones. The laminae are, generally, of a coarse grain, and the globular figure considerably mutilated. In short, it may be said to possess every variety of appearance which different degrees of mechanical compression, exerted on a sphere, can possibly effect; and the remark applies equally to the spheroidal basaltes of the southern parts of Europe, and other districts where such minerals prevail. [pp. 144-146]
Group of Basaltic Columns