90 



siiliei-oiJ, miglit lead to the inference that the difTusion of its lime has in some 

 way determined a fresh arrangement of the particles of the -whole, bxit such 

 centres are frequently altogether absent and the larger nodules often show 

 no appearance of having ever contained any exceptional quality of organic 

 remains. 



Especially observable is the fact that the shape of nodules is found 

 frequently to depend on some external features of the masses of stone in which 

 they occur, such as faults or joints. In a word, the weather staining seems to 

 foreshadow the nodule. Besides, there is some reason to think that the coloura- 

 tion accompanying weather staining is sometimes accompanied by a ^jhysical as 

 well as a chemical difference, such as that between sand and clay, between cal- 

 careous and argillaceous stone. 



Do not these facts point to an external origin of this spheroidal structure, 

 and suggest the probability that the infiltration of moisture from all points of 

 the surface of a block of stone may, together with some accompanying chemical 

 or molecular action, drive inwards the more soluble constituents of the mass, 

 and thus arrange the whole in concentric layers, and produce in many cases a 

 central nodule ? 



Do they not suggest that where some crystallizable substance, such as 

 carbonate of lime, is diffused through a mass of stone it may be gradually con- 

 centrated at one spot, either by the action of some external agent, like water 

 soaking through the pores, or by some internal molecular attraction ? Another 

 link may thus be obtained in the proof of that constant energy which is ever 

 working in the apparently unalterable crust of our earth, re-arranging its con- 

 stituents and even in some cases accumulating the metals in certain veins and 

 nodules. 



(The paper was well illustrated by a series of clever sketches.) 



Mr. Lawrence, of Pontypool, and one or two other gentlemen present, 

 had observed instances of spheroidal structure in rocks, and the question was 

 asked as to whether the common nodules of ironstone were due to the same 

 action ? 



Mr. La Touche thought they might be so, and after some further explana- 

 tion, ho said that he had sent a copy of his paper to the Rev. Professor Haughton, 

 of the Dublin University, who had kindly returned the following answer :— 



"I am familiar with similar ellipooirial structures in our Irisli coal shales in Queen's 

 County, but thoy do not seem to bo so well developed as tliose shown in your drawings. 

 I believe that all rocks when formed and subjected to varying pressure from the surround- 

 ing mass have developed within them a latent ellipsoidal stnicture ; this is shown by the 

 distortion of fossils and other considerations. I published a paper in the Philusopliieal 

 Mwja-rme some years ac,o on tliis subject (185rt or ISfiT), and showed how the ages of the 

 elliijsoid mi^'ht be calculated from the shape of the distorteil fossils. The weathering of 

 the rock developes the latmt structure, in a manner like that of the structure developed 

 by weathering at the angles of the basaltic columns. I shiU have pleasure (with your 

 permission) in laying your sketches and letter before the Geological Society of Ireland in 

 November ne,\t." 



