1823.] the principal Mountain Chains of Europe. 283 



correspondence, however, may certainly be traced on the oppo- 

 site shores of the British channel, and there seem to be strong 

 indications of the same kind in the Jura chain. 



Distribution of this Series. 



(A.) England. 



A line drawn from the north-east of Yorkshire to the south- 

 west of Dorsetshire will nearly indicate the western and inferior 

 limit of this series. The lias, however, extends westwards from 

 this boundary on both sides the British Channel in Somerset- 

 shire and Glamorganshire. The eastern and superior limit 

 follows a line nearly parallel to the former, and between 20 and 

 41 miles to the south-east of it. The three systems of oolites 

 form as many parallel ridges of hills separated by intermediate 

 valleys, following the course of the intermediate clays. The 

 great or third oolitic system forms the most extensive and con- 

 tinuous of these ranges. The chains presented by the other two 

 are more partial, and interrupted through considerable intervals. 



(B.) Other British Islands. 



The British Islands present no traces of these formations 

 beyond the limits above assigned, with the exception of the lias, 

 which occurs in Ireland in the county of Antrim, near the south- 

 east border of the basaltic district ; in the Isle of Sky, and some 

 other of the Hebrides. 



(C.) France. 



1. In the Denudation of Boulogne. — The escarpment of the 

 chalk sweeps round a semicircular tract, in the centre of which 

 this town is placed, with a radius of about 12 miles distance. 

 The green sand follows the fort of this escarpment, and may 

 also be traced on the north-east of Uissant, and the hills close 

 to Boulogne, on which Buonaparte's tower is built, are capped 

 with strata of ferruginous sand, possibly our own iron sand. 

 But instead of these formations occupying, as in the corres- 

 ponding tract in Kent and Sussex on the English side, the 

 whole of the denuded area, we find the coast, through the 

 greater part of its breadth, lined with a calcareo-argillaceous 

 formation which underlies the sand last mentioned ; this may 

 be studied in the cliffs on either side of Boulogne, which, how- 

 ever, are, from the nature of the material, in a very crumbling 

 state. 



One of the upper beds of this formation consists of a remark- 

 able calcareo-siliceous grit. Boulogne is principally built of 

 this rock. It often forms the upper stratum of the cliffs on the 

 north-east of that town, and is particularly abundant at a place 

 called le Creche, between it and Uissant. This rests on some 

 beds of argillaceous limestone, separated by clay ; and along the 



