14 



made to the Silurian system, that it wanted a definite base, and was 

 not distinctly separated from the Cambrian system ; this was not over- 

 looked by Mr, Murchison, who states that the line drawn between 

 the two systems was provisional. The difficulty arose from classing 

 with the Cambrian system many beds belonging both to the Upper 

 and the Lower Silurians, and it will vanish when this is corrected ; 

 the lower boundary of the Silurian system will then prove as distinct 

 in North Wales as in Westmoreland and Cumberland ; but to pro- 

 duce this result, the country west of Llangollen and Welsh Pool 

 must be remapped. Of the district now coloured as Upper Cambrian 

 a small share will be given to the Ludlow and Wenlock formations, 

 a larger portion to the Lower Silurians, and certain central bosses 

 of older rocks will remain for the Cambrian system : but the Uj^per 

 Cambrian of Professor Sedgwick, and its representative in Mr. 

 Greenough's nomenclature, the upper division of the Lower Killas, 

 must be struck out of our tables, and the Lower Silurians made to 

 rest on the true Cambrian rocks. 



The igneous rocks of Arenig and Arran Mowddy are described as 

 varying compounds of felspar and quartz. The two chains bear 

 nearly north, and their eruption is supposed by the author to have 

 modified the face of the countrj'^, and to have caused much of its pre- 

 sent complication, the prevailing strike previously having been N.N.E. 

 In the absence of direct evidence on the subject, Mr. Sharpe en- 

 deavoui's to prove that Arenig and Airan Mowddy are at least as 

 modern as the Ludlov/ rocks, by showing that the upheaving of 

 these chains has broken up the parallelism of the cleavage planes 

 of the slaty rocks resting on them : assuming that these planes had 

 originally a constant direction in each district, their dislocation at 

 any spot would show that it had been disturbed subsequently to the 

 cessation of the cleavage process, and we may thus class igneous 

 eruptions as prior to, or posterior to, the cleavage ; and may then 

 connect them with the deposition of the formations, by observing 

 at what epoch the cleavage ceased in the district. In North Wales 

 and in Westmoreland, the cleavage only reaches into the Lower 

 Ludlow formation ; in Devonshire and Cornwall it continued later : 

 therefore Arenig and Arran Mowddy must have been upheaved after 

 the epoch of the Lower Ludlow shale. 



The memoir concludes with a general list of the species of fossils 

 found near Bala. 



" Notice on the discovery of the Remains of Insects in the Lias 

 of Gloucestershire, with some remarks on the Lower Members of 

 this Formation." By the Rev. P. B. Brodie, F.G.S. 



The lower beds of the lias, in which these organic remains occur, 

 are extensively developed in the neighbourhood of Gloucester and 

 Cheltenham, and occupy the greater part of the vale. In the upper 

 part of the lower beds, in a hard blue limestone, was found the ely- 

 tron of a coleopterous insect of the family Buprestidee, apparently a 

 species of Ancyloclmra of Escholtz. This was the only fossil of the 

 kind met with by Mr. Brodie in this portion of the lias. With this 



