384 Correspondence — Concretions. — MisceHaneons. 



wanting (as in nearly every borehole nortli of the Tees) ; (2) the 

 Salt-rock is absent and the Eed Marl overlying its horizon is not 

 'rotten marl' but compact; (3) the Magnesian Limestone (299 feet) 

 is the thinnest complete section in County Durham ; (4) no coal is 

 found ; (5) the Yoredale Rocks are represented by 336^ feet of grey 

 sandstones and encrinital limestones, carbonaceous shales, ironstone 

 nodules and carbonaceous sandstones. 



An Appendix, containing full details of the two vertical sections, 

 accompanies the paper. 



coiaE,ss:F>03srzDEiNrGE. 



CONCRETIONS. 



Sir, — Is not carbonic acid evolved from decaying orgaBisms ? 

 If lime were present in the water in which such decomposition were 

 taking place, would not the acid combine with the base to form a 

 carbonate of lime ? 



Would not the precipitation of this salt first take place immediately 

 around the organic nucleus, and form a covering which would 

 enclose the decomposing matter ? This covering would not only 

 retard future chemical action, but would confine it to a much 

 narrower limit, viz. the centre of the embryonic concretion. 



But as the decomposition of the organic matter would not neces- 

 sarily at this stage be arrested, would not the CO2 gradually ooze 

 through the thin crust, and the chemical action continue, though 

 more slowly, as before, causing a gradual thickening of the concretion 

 through external precipitation. 



The greater the distance from the nucleus, the weaker would this 

 action become, and the concretion would finally reach a point at 

 which — owing either to a failure in the supply of the CO.,, or the 

 inability of the same to penetrate the increased thickness of CaCOj — 

 it would cease to grow. 



Would not this theory account for the formation of Spliaosiderites, 

 and other nodules containing organic nuclei ? Would it not also 

 explain why these so often increase in hardness towards their 

 centres ? C. C. W. 



3vniscEXjijjL3sr:EOTJ3, 



York Museum. — We learn from York that the late Mr. William 

 Reed, F.G.S., whose obituary notice we published in our June Number 

 (p. 283), has most generously bequeathed to the Yorkshire Philo- 

 sophical Society the sum of £600 the interest of which is to be 

 expended on the Museum which has already been so greatly enriched 

 by the various donations of collections presented by Mr. Reed in 

 past years. 



