J. W. JUDD ON THE SECONDARY ROCKS OF SCOTLAND. 733 



As affording indications of the existence of an old beach of the 

 Cretaceous sea, these beds of Gribun and Inch Kenneth are of very 

 great interest to the geologist ; and, but for the occurrence of the 

 characteristic fossils in their upper part, it would be impossible to 

 discriminate the beds of pebbles which compose them from those of 

 the underlying Poikilitic series, the reconstructed materials of which 

 form so large a proportion of their mass. 



b. The Strata representing the Challc. 



In speaking of the Upper-Greensand beds we have already had 

 occasion to notice the small masses of altered Chalk at Carsaig and 

 Gribun. Although converted into a siliceous rock, the fact that 

 this chalk was originally calcareous (that is, made up of shells of 

 Eoraminifera, with fragments of Inoceramus and other organisms 

 common in the English Chalk) is made perfectly clear by the study 

 of thin sections of the rock by the aid of the microscope. In this 

 examination of the Scottish Chalk, I have received much aid and 

 many valuable suggestions from my friends Professors W. K. Parker 

 and T. Kupert Jones. To the latter I am indebted for the note on 

 the organisms occurring in a series of sections which I had prepared 

 of these rocks, which is printed at the end of this paper (p. 739). 



Although there are several other points in the island of Mull at 

 which strata probably belonging to different parts of the Upper Cre- 

 taceous occur, yet at all these places the relations of the beds are so 

 obscure, or their characters have been so completely modified by the 

 influence of the great volcanic masses in their neighbourhood, that 

 it would not be safe to pronounce with confidence on the age of any 

 of them. 



In Morvern, however, the characters and relations of the strata 

 representing the Chalk can be more perfectly made out. On both 

 sides of Loch xiline and along the south shore of Loch Arienas the 

 Greensand strata are covered by thick masses of coarse white sand- 

 stone, locally assuming variegated tints. These contain no fossils, 

 but from their stratigraphical relations can be safely correlated with 

 the Middle and Lower Chalk of England. This mass of sandstone 

 strata varies greatly in thickness and characters, but seldom, if ever, 

 exceeds 100 feet. It contains no fossils, but exhibits evidence of 

 having been accumulated under estuarine conditions. 



The most interesting of all the sections of the representatives of 

 the Chalk strata, however, are those which occur beneath the 

 singular outlying masses of Beinn-y-Hun and Beinn-y-Hattan, in the 

 same district of Morvern, where they are preserved by the singular acci- 

 dent already described. (See the section, Plate XXXI. fig. 2.) There 

 are, however, only a few points along the lines of outcrop of these 

 beds where the succession of strata can be satisfactorily made out. 



In Beinn-y-Hun the masses of coarse estuarine Sandstone repre- 

 senting the Lower and Middle members of the Chalk are fairly well 

 seen, and are probably nearly 100 feet in thickness. In the midst 

 of these sandstones Macculloch found a thin seam of lignite or coal ; 



