46 Correspondence — Mr. Alex. Somervail. 



infers, tlierefore, that when the river began to erode its channel, the 

 plateau was relatively lower than the tract to the south of the 

 present course of the stream, but that by denudation the relations 

 have been reversed, whilst the river has never left its originally 

 selected course. 



The author compares the state of things with that which must 

 have occurred in the case of the northerly rivers running from the 

 centre of the Wealden axis ; but mentions that Prof. Safford and 

 Mr. J. Leslie account for the Cumberland plateau b}' faulting, though 

 he thinks that the well-defined escarpment along the valley of East 

 Tennessee seems to show that this cause is insufficient. 



In conclusion, he believes that the denudation was accelerated 

 during the pluvial or " Champlain " period, and calls attention to 

 the " Columbia formation " on the east side of the Alleghanies, and 

 to the deposit of red loam by which the surface of the country of the 

 valleys of the Tennessee and Sequachee is overspread, and which is 

 probably referable to a similar stage. 



3. " On certain Ornithosauriau and Dinosaurian Eemains." By 

 E. Lydekker, Esq., B.A., F.G.S. 



The author is indebted to Professor 0. C. Marsh for the correct 

 determination of the bones described in the paper. 



1. Ornithosaurian Quadrates. — The reptilian bones in the British 

 Museum, Nos. 43034, 44183, and 41179, are Ornithosaurian quad- 

 rates. The two latter belonged to the right side of the skull. The 

 distal extremity of each forms a deeply grooved oblique trochlea, 

 above which is a nearly quadrangular shaft. To the inner side of 

 this shaft is attached, by suture, a flattened plate of bone, concave 

 internally, and convex externally, representing part of the pterygoid ; 

 so that the relation of the quadrate to the pterygoid in the Ornitho- 

 saiiria is the same as in the RhyncJiocephalia. 



The smaller quadrate would agree approximately in relative size 

 with the so-called Pterodactylxis Manseli, Owen, and the larger more 

 nearly with the so-called Pt. siiprajurensis, Sauvage, both of which 

 may be provisionally referred to Ehnmphorhynchus. 



2. Tibia of Coeluroid Dinosaur. — The author would provisionally 

 refer the right tibia of a small Dinosaur from the Wealden of the 

 Isle of Wight, which had been incorrectly referred to HypsHopJiodon, 

 to the species originally described, from an examination of two 

 vertebrae, as Calamospondylus Foxi, but which he would now name 

 Calamosaurus Foxi. It presents striking avian affinities. 



coI^I^Es:po^:^^IDSITGE! , 



PROF. BONNEY AND GENERAL McMAHON ON THE GEOLOGY OF 

 THE LIZAED DISTRICT. 

 SiK, — In your last issue, Prof. Bonney in his characteristic style 

 refers to my late work in this district. He, however, at once, falls 

 into error as to the number of my communications to the Magazine. 

 there being five, not four as stated by him. The one he overlooks 



