90 REPORT— 1871. 



that still further and vaster denudation took place before the setting in of the Ice- 

 age ; and finaUy, that the deposits of that age have since been to a large extent 

 removed. AVith the proofs, therefore, of such continued destruction, it would be 

 vain to look for any aboriginal outline of the surface, or hope to find any of the 

 later but still early features of the landscape remaining permanent amid the sur- 

 rounding waste. 



In the second place we note that, in the midst of this greatly denuded area, it 

 is the harder rocks which form the hills and crags. Those masses which in the 

 long process of waste presented most resistance to the powers of destruction, are 

 just those which, as we might expect, rise into eminences, while those whose re- 

 sistance was least sink into plains and -(-aUej-s. ALL the craggy heights which 

 form so conspicuous a feature of Edinburgh and its neighbourliood, are composed 

 of hard igneous rocks, the undulating lowlands lie upon soft aqueous rocks. 



In the third place, the coincidence of the position of hills and crags with the 

 existence of ancient igneous rocks, cannot be misinterpreted by ascribing the pre- 

 sence and form of the hills to the outlines assumed by the igneous material ejected 

 to the surface from below. The hiUs are not due to igneous upheaval at all, but 

 can be shown to have been buried deep under subsequent accumulations, to have 

 been bent and broken with all the bendings and brcalcs these later formations un- 

 derwent, and to have been finally brouglit to light again only after a long cycle of 

 denudation had removed the mass of rock under which they had been concealed. 

 What is true of the hills of Edinburgh, is true also of all the older volcanic districts 

 o j Britain. Even where the hills consist of volcanic rocks, their existence, as 

 hills, can be proved to be one of tlie results not of upheaval but of denudation. 



In the fom-th place, this district furnishes an instructive illustration of the in- 

 fluence of faults upon the external contour of a country. The faults here do not 

 form valleys. On the contrary, the vallej's have been cut across them in innu- 

 merable instances. In the liallieith coal-field, for example, the valleys and ra- 

 vines of tlie river Esk travei-se faults of 190 to nearlj' .500 feet, yet there is no in- 

 equality at the surface, the whole ground having been planed down by denudation 

 to one common level. "When, however, a fault brings together rocks which differ 

 mucli in their relative powers of resistance to waste, tlie side of the dislocation 

 occupied by the harder rocks will tend to form an eminence, while the opposite 

 side, consisting of softer rocks, will be worn down into a hollow or plain. Con- 

 spicuous examples are furnished by the faults which, along the flanks of the Pent- 

 land Hills, have brought down the comparatively dcstnictible sandstones and 

 shales of the Carboniferous series, against the much less easily destroyed porphy- 

 rites and conglomerates of the Old Red Sandstone. 



In fine, we learn here as elsewhere in oiu' country, and here more strikingly 

 than often elsewhere, on account of the varied geological structure of the district, 

 that the present landscape has resulted from a long course of sculpturing, and that 

 how much soever that process may have been accelerated or retarded by underground 

 movements, it is b}' the slow but irresistible action of rain and frost, springs, ice, 

 and the sea, that out of the various geological formations among which Edinburgh 

 lies, her picturesque outline of hill and valley, crag and ravine, has, step by step, 

 been carved. 



The YorTcshire Lias and the Distribution of its Ammonites. 

 Btj the KeV. J. F. Blake. 



The Lias of Yorkshire is exposed on the coast for a distance of about 30 miles, 

 and owing to faults and undulations the series is repeated twice, one main area 

 being to the north, the other to the south of Whitby ; and there are two outlying 

 patches, one of the highest beds at Peak, the other of the lowest beds at Eedcai-. 



The basis of the description in this paper is the division into Ammonite zones, 

 as by Oppel and others. 



1. Zone of Ammonites Jurensis. — These occur at Peak. The author has not found 

 the characteristic Ammonite in situ, but recognizes the zone by its peculiar fauna. 

 It appears to be divided into an upper and lower division. 



