TRANSACTIONS OP SECTION C. 753 



G. JIuxleyana, G. Duffiana, and G. Juddiana. Another dicynodont more nearly 

 related to the Ptychognathus of Owen, hut with a short muzzle and no teeth, has 

 been named Geikia El(/inensis. 



The peculiar horned reptile, resembling the Moloch lizard, but apparently most 

 nearly related lo the South African Pareiasaurus, has been named Elginia 

 mirabilis. 



Work among the Elgin reptiles is still going on, and two entirely new forms 

 are now made known for the first time. One of these was found by Mr. James 

 Grant, of Lossiemouth; and, although the exact locality is uncertain, there is no 

 doubt as to its being from the sandstone of the Elgin area. This specimen, which 

 includes the skull (about three inches long) and the front part of the tnink, is evi- 

 dently related to Stagonolepis. 



The second new form was obtained by the Eev. Dr. Gordon from the EVin 

 ■Sandstone of Spynie Quarry, and will eventually be preserved in the British 

 Museum. With the exception of the fore limbs and neck, nearly the whole of the 

 skeleton has been preserved. Much of the skull has been very successfully cleared 

 from the matrix by Mr. Richard Hall, of the British Museum, and was exhibited 

 at a soiree of the Royal Society, when its resemblance to Aetosaurus was pointed 

 out by Mr. Arthur Smith Woodward. This reptile is of much interest, as it seems 

 to be a form intermediate between the crocodiles and dinosaurs, being, apparently, 

 related on the one hand to the Parasuchia and on the other to the theropodous 

 dinosaurs. The skull is, in fact, that of a miniature megalosaur. 



FRIBA Y, SEPTEMBER 15. 

 The following Papers and Reports were read : — 



1. A joint Discussion ivith Section E on the Limits of Oeology and 

 GeograjjJiy took place, (See p. SSL) 



2. The Dissected Volcano of Grandall Basin, Wyoming. 

 By Professor Joseph Paxson Iddings. 



The writer in exploring the north-eastern corner of the Yellowstone National 

 Park and the country east of it came upon evidences of a great volcano which had 

 been eroded in such a manner as to expose the geological structure of its basal 

 portion. 



The work was carried on as a part of the survey of this region under the charge 

 of Mr. Arnold Hague, of the United States Geological Survey. This paper is an 

 extract from a chapter in the final report on the Yellowstone National Park in pro- 

 cess of completion, and the writer is indebted to Major J. W. Powell, Director of 

 the Survey, and to Mr. Hague, chief of the division, for permission to present it at 

 this time in anticipation of the publication of the final report. 



The area of volcanic rocks described is but a small portion of the great belt of 

 igneous material that forms the mountains of the Absaroka range, lying along the 

 eastern margin of the Yellowstone Park. The volcano of Grandall Basin is one of 

 a chain of volcanic centres situated along the northern and eastern borders of the 

 Yellowstone Park, which are all distinguished by a greater or less development of 

 radiatintr dikes, and by a crystalline core eroded to a variable extent. 



The Palaeozoic and Mesozoic strata which formed an almost continuous series 

 to the coal-bearing Laramie had been greatly disturbed, and almost completely 

 eroded in places, before the volcanic ejectamenta in this vicinity were thrown upon 

 them. The period of their eruption is therefore post-Laramie, presumably early 

 Tertiary. 



The first eruptions of andesite were followed by those of basalt in great quan- 

 tities, and these by others of andesite and basalt like the first. This was succeeded 

 1893. 3 c 



