66 REPORT — 1856. 



areas, would induce the conclusion that they result from some uniform cause operating 

 over a great space. 



The theory which attributes joints to shrinkage would not be sufficient to account 

 for these master-joints. 



These seem rather to have originated from the application of a mechanical force 

 applied in one direction. This force was probably that which gave the middle and 

 upper palaeozoic strata of the south of Ireland their east and west strike of rolls, — the 

 force being apphed either to the north or south, the rocks having a tendency to extend 

 themselves at right angles to the direction of the force, and consequently breaking, 

 from their rigidity, into parallel lines which we recognize as joints. The origin of 

 the other two forms of jointing is by no means apparent, but this may probably have 

 been the same cause operating locally in different directions at a subsequent period to 

 that which produced the master-joints. 



On the Lignites of the Giant's Causeway and the Isle of Mull. 

 By Professor Harkness, F.G.S. 



The Giant's Causeway affords, in connexion with its basalts, beds of lignite, and in 

 the Isle of Mull we have the same circumstances occurring. The lignite of the former 

 locality retains its woody nature to a great extent, and this exhibits sufficient of its 

 original structure to admit of the determination of the forms of vegetables to which 

 this substance owes its origin. The only changes which the structure of this substance 

 has undergone, result from compression, which has brought the sides of the woody 

 cells in immediate contact, and in some instances so lacerated the tissue as to give 

 this, in longitudinal section, a somewhat spiral arrangement. Sometimes, however, 

 the longitudinal section gives this tissue in its perfect state, and when this is the case, 

 pitted vessels, of a coniferous character, are seen on the sides of the cells. 



The size of these cells, and their relative distance from each other, would lead to the 

 conclusion that the trees forming this lignite are nearly allied to those which are found 

 forming the mass of lignite mentioned by His Grace the Duke of Argyll as occurring 

 associated with the basalts of the Island of Mull. In the latter locality the lignite 

 presents itself in two conditions, the one in a state of nearly pure coal, the other 

 having more of a woody aspect. 



The vegetable fibre of the Mull lignites is often sufficiently distinct to manifest its 

 internal structure, and would support the inference as to the similarity in age of these 

 deposits, and those of the Giant's Causeway. The fossil evidence, as this is shown 

 by the nature of the lignites, supports the conclusion of His Grace the Duke of 

 Argyll, adopted by Sir Charles Lyell, that the traps of Mull and the Giant's Cause- 

 way belong to the same geological epoch, that epoch being the Miocene. 



On the Relative Distribution of Land and Water as affecting Climate at 

 different Geological Epochs. By Professor Hennessy, M.R.I. A. 

 The views developed in this paper were partly deduced from the principles advanced 

 by the author in his memoir on isothermal lines. As all the investigations on terres- 

 trial temperatures which he has undertaken will be printed elsewhere, it is unnecessary 

 to do more than state some of the conclusions of this paper. 



1. The distribution of land and water most favourable to high general terrestrial 

 temperature all over the globe is that of the existence of land, not in great continents, 

 but in islands evenly distributed over the earth's surface. 



2. Under such conditions the isothermal lines in the islands would generally 

 approach the character of closed curves, and the temperature in the higher latitudes 

 would decrease in advancing from the coasts to the interior of an island. 



3. If these views are correct, some differences might be expected between some of 

 the fossils representing the organized beings of the interior of such islands, and those 

 distributed about the coasts. ^ 



Notice of some Minerals from the Isle of St. Thomas. 

 By Dr. H. B. Hoknbeck. 



