Vol. 69.] TWO DEEP BORINGS AT CALVERT STATION. 329 



Natural gas occurs in the salt-bearing Trias (Keuper) of Durham, 

 where it overlies the Permian Magnesian Limestone : — 



'The presence of bitumen, rock-oil, inflammable gases, or hydrogen sulphide 

 in the [Keuper] beds below the salt is often assumed to indicate underlying 

 Coal Measures from which they are supposed to be derived. But this inference 

 has proved erroneous again and again on. Tees-side.' 1 



With this warning before us, it may seem very rash to suggest 

 that the Calvert gas may have leaked into porous Triassic strata 

 from underlying Coal Measures, possibly at some distance to the 

 west or north-west. We only mention it here as a possibility, 

 the less unlikely in view of the published analysis, 2 which shows 

 the Calvert gas to resemble that obtained from Wigan cannel-coal. 



III. PalIeontolooical Notes. [A. M. D.] 

 Nuculana cf. auENSTEDTi (Tate). 



Leda qitenstedti R. Tate, 1870. ' List of Irish Liassic Fossils ' App. I, 7th 

 Ann. Rep. Belfast Nat. F.-C. p. 19 & pi. i, tig. 4. 



These forms occurred at several horizons between 203 and 

 300 feet {algovianum to striatum zones) — showing very slight 

 variations, which may possibly prove to have zonal value. They 

 are smooth shells, with very delicate growth-striations, rounded 

 in front, and with only the slightest tendency to rostration 

 behind. Such forms have been, in England, commonly identified 

 as Leda galatea d'Orb., without sufficient justification, as no 

 figure or adequate description of that species was given by 

 A. d'Orbigny. 3 They are very near to Dr. Kitchin's ' sp. P> ' from 

 the cccpricornus zone of the lirabourne Boring/ but differ slightly 

 in proportion of height to length. They are not identical with 

 Tate's species, which is Hettangian ; but, pending a more careful 

 zonal study than can now be given to them, it is undesirable to 

 propose a new name. 



Orbiculoidea aff. holdent (Tate). (Fig. 2, p. 330.) 



Distinct holdeni R. Tate, 1867. Q. J. Gr. S. vol. xxiii, p. 314. 

 Distinct holdeni Tate, 1874. Davidson, ' Brit. Foss. Brach. Suppl. Jur. & 

 Triass. Brach.' Monogr. Pal. Soe. p. 85 & pi. x, tigs. 12-12 c, pi. xi, fig. 32. 



This little brachiopod is represented only by a number of 

 immature brachial valves, the largest of which are about 3-5 mm. 



1 T. Tate, ' Notes on Recent Borings for Salt & Coal in the Tees District' 

 Q. J. G. S. vol. xlviii (1892) p. 489. 



2 ' Iron & Coal-Trades Review ' Sept. 1st, 1911, pp. 316, 317. 



3 [M. A. Thevenin, who is figuring the types of d'Orbigny's " Prodrome" in 

 the ' Annales de Paleontologie' has kindly written to inform me that the type 

 of Leda galatea is broken in front, and to express the opinion that Dumortier's 

 figure should be taken as the type ('Etudes paleont. sur les Terr. Jurass. du 

 Bassin du Rhone ' pt. 3, 1869, p. 120 & pi. six, figs. 5, 6). Those figures in- 

 dicate a form related to, but by no means identical with, the Calvert and 

 Brabourne specimens. — A. M. D., June 12th, 1913.] 



4 Nuculana 3p. B, F. L. ICitchin, 1911 : ' Mesozoic Rocks in some of the 

 Coal-Explorations in Kent' Mem. Gfeol. Surv. p. 175. 



