'26 



J. W. JTTDD ON THE SECONDAKY ROCEE OE SCOTLAND. 



and the northern part of the Inner Hebrides, rrmst have originally 

 constituted a great formation comparable to the Wealden of the 

 south-east of England in the thickness of its strata and the area 

 which it covered. Like the Wealden, too, it was only developed 

 over a somewhat limited area, being due to conditions that could 

 not be expected to extend far. Hence the purely Estuarine infra- 

 Oxfordian delta must be regarded, like its Neocomian analogue, as 

 constituting an entirely local and exceptional phenomenon. And, 

 though the fragments preserved to us by such remarkable accidents, 

 both on the east and west coasts of Scotland, can only be regarded 

 as forming a series of very minute vestiges of this great formation, 

 we must bear in mind that in the southern part of the British area 

 it was represented by strata of much less thickness, which were 

 almost uniformly of marine origin. 



It is, however, worthy of remark that it is where the Great Estua- 

 rine Series attains its greatest thickness and fullest development that 

 it is suddenly cut off by the overlap of the Upper-Cretaceous rocks. 



g. The Oxford Clay. 



Immediately overlying the great series of estuarine strata just 

 described, we find, both in Skye and Eigg, a mass of blue clays 

 containing some subordinate bands of argillaceous limestone, 

 which are undoubtedly of marine origin. The age of this set of 

 clays is fortunately placed beyond doubt by the nature of the 

 fossils which they yield ; for these clearly represent the fauna of the 

 middle portion of the Oxford Clay — the zone of Ammonites cor- 

 datus. 



The fossils of these strata, which are tolerably numerous, but by 

 no means well preserved, have been examined by Prof. Ed. Forbes, 

 who gives a list of the forms obtained by himself from Loch Staffin ; 

 and by Mr. Tate, who enumerates those found by Dr. Bryce at Uig. 

 It will be interesting to give, for comparison with these, the follow- 

 ing list of species, collected either by myself or Mr. Hugh Miller at 

 the Bay of Laig, in the island of Eigg : — 



Fossils of the Oxford- Clay Beds from the Bay of Laig, Island 

 of Eigg. 



Belemnites sulcatus, Mill. 



gracilis, Phill. 



Ammonites Williamsoni, Phill. ( = A. 



arduennensis, D' Orb.). 



Toucasianus, D' Orb. 



■ cordatus, Sow. (Several varieties 



of this species are very abundant.) 

 — — excavatus, Sow. 



Mariee, If Orb. 



Lamberti, Sow. 



Sutherlandise, Sow. Young forms. 



Ostrea Koemeri, 

 Avicula expansa, Phill. 



braamburiensis, Sow. 



Area, ?sp. 

 Nucua, sp. 

 Lucina, ?sp. 



Astarte (near A. minima, Phill.). 

 Serpula. 



Dorsal spine of fish. 

 Wood and vegetable remains abun- 

 dant. 



The Oxford-Clay strata of the "Western Isles are nowhere well 



