ANNIVERSARY ADDRESS OF THE PRESIDENT. CXXXV11 



land, and as, in its lowest and middle divisions, it attains a thick- 

 ness of 1500 feet, it compensates for the small area by the important 

 reflections to which it may well give rise in respect to its former 

 physical conditions, as so deep a deposit in so small a space mnst be 

 considered only a relic of a much greater whole ; and we may well 

 say, with Mr. Geikie, that the intricate and confused character of the 

 geological structure of Skye gives to the liassic beds an additional 

 and peculiar interest. Considering the state of knowledge at the 

 time when Macculloch published his ' Western Islands/ and the im- 

 perfect maps he had to guide him in his researches, we may well 

 excuse some errors in marking the limits of strata, even in so acute 

 and able an observer ; and it is therefore no real disparagement to 

 him that others have since been able to discover and correct them. 



As a fact it is remarkable, that the Lias in Scotland rests on either 

 a metamorphic or palaeozoic base, usually the Old Red Sandstone, and 

 that it is confined to the northern counties, among the hypogene and 

 older palaeozoic districts. The lias of Skye is sometimes conformable 

 and sometimes unconformable to the underlying red sandstone, a 

 purplish-grey quartz-rock ; but, as these rocks have hitherto yielded 

 no organic remains, it cannot be positively determined whether they 

 belong to the Old Eed, the Silurian, or the later portions of the 

 gneissose series of Central Scotland. 



Mr. Geikie traces the limits of the sedimentary deposits, and 

 describes their mineral character as well as their organic relations, 

 and then in a similar manner notices the various igneous or erupted 

 rocks, which have, without doubt, given rise to much of the com- 

 plexity of the district. This paper is accompanied by a very valuable 

 list of the fossils collected by Mr. Geikie from the lias, drawn up by 

 Dr. Thomas Wright, who prefaces the list by a brief definition of the 

 sense in which he understands the term " Middle Lias." He here 

 repeats his former opinion, that the terms Upper Lias, Middle Lias, 

 and Lower Lias, as used by English geologists, require modification, 

 in order to place the " basic" beds in correlation with those of French 

 and German authors, — modifications which in his opinion require the 

 basic beds of the Inferior Oolite to be transferred to the Lias, as the 

 " Upper Lias Sands," and the beds which, with the Marlstone, were 

 the upper beds of the Lower Lias, to be considered the basic beds of 

 the Middle Lias. 



Following up this idea, Dr. Wright gives a table showing the con- 

 dition of the lias-beds in France, Germany, Gloucestershire, and Skye, 

 in which these alterations are exhibited. This is a disputed point, 

 to which I shall again have to refer. I shall :only further observe 

 that Dr. Wright first gives a list of about 86 characteristic species of 

 Mollusca and Eadiata of Gloucestershire, and then compares those 

 collected by Mr. Geikie, which are identified (as already-described 

 species) with them. These are principally from the shales of Pabba, 

 which Dr. Wright, as the result of the comparison, places at the 

 base of the Middle Lias, under the Marlstone. As there are 25 of 

 such Pabba species, the deduction is made from a more enlarged 

 basis of comparison than in the case noticed in my last address, and 



