1873.] DAWSON LEPT0PHL02EM RTIOMBICEM ETC. 3G9 



Mr. Forbes, whilst admitting that in many instances Clay-iron- 

 stones had been deposited in circumscribed waters or shallow lakes, 

 as is the case with the lake iron-ores in Sweden now actually in 

 process of formation, pointed out that some of the largest Clay-iron- 

 stone deposits in England — those of the Yoredale series — contained 

 marine fossils in abundance. On chemical grounds it is not clear 

 in what state of combination the author imagines the iron to have 

 been held in solution previously to being, according to him, con- 

 verted into carbonate of iron, by meeting with the carbonic acid 

 formed in the lagoons from decomposing vegetable matter ; and 

 further, the mere fact that the Saltburn mud effervesced with 

 nitric acid after having been bottled for some days, must not be 

 regarded as necessarily proving the formation of carbonate of iron 

 in it. 



Mr. Charlesworth called attention to the nodules of ironstone 

 which were found in the coprolite diggings in Suffolk, as to the 

 origin of which little was known. The banding in the interior of 

 these nodules was posterior to their formation, as was evinced by its 

 following the contours of the exterior, and even of lithodomous 

 borings in them. 



4. Note in vindication of Leptophlceem KrroMBicEM and Lepidoden- 

 dron GAsriANEM. By Principal Dawson, LL.D., E.R.S., E.G.S. 



[Abridged.] 



The author forwarded to the Society photographs illustrating his 

 species Lcptophlceum rhombicum and Lepidodendron gaspianmn, with 

 the view of showing that they are specifically and gcnerically distinct, 

 and also distinct from the plant identified with them by Mr. Car- 

 ruthcrs*, and from Lepidodendron nothum of linger -j-, to which 

 species Mr. Carruthers referred the whole series of specimens, both 

 from Australia and Eastern North America. 



Dr. Dawson states that, though he has not seen Ungcr's specimens, 

 he has carefully studied that author's figures and descriptions of 

 Lepidodendron nothum ; and in the original description of L. gas- 

 pianum % he indicated that it is allied to L. nothum, although he 

 regarded it as specifically distinct. He considers that L. nothum is 

 not at all near to his Leptophlceum rhombicum, and that a comparison 

 of Unger's figure or Mr. Carruthers's figure of Mr. Daintree's plant 

 with the photographs of L. rhombieum will show that there is not 

 even a generic connexion between them. 



To show the want of identity between Leptophlceum rhombieum 

 and Lepidodendron gaspianum, Dr. Dawson sums up their characters 

 as follows : — 



* Quart. Journ. Geol. Soc. vol. xxviii. pp. 351-353. 



t Denkschr. Akad. Wiss. Wien, matk.-naturw. CI. vol. xi. (1856) p. 175. 



I Quart. Journ. Geol. Soc. vol. xv. p. 483. 



