1820,] Geological Sociefj/. 453 



here contains beds of iron ore associated with brown spar, Sec. 

 These furnish the iron ore worked in the forest, the coal mea- 

 sures being ahnost destitute of that mineral. The coal formation 

 which occupies the highest place in this basin includes in all 22 

 beds of coal alternating with slate clay and various sandstones, 

 the total thickness of the formation being about 800 yards. In 

 this part of the memoir, the authors profess to derive the most 

 important parts of their iuforniation from Mr. Mushet's section. 



The horizontal and overlying strata are next described. These 

 consist of 1 , extensive beds of a conglomerate, containing rolled 

 and angular fragments derived from the partial destruction of the 

 older neighbouring rocks, and, therefore, containing in this dis- 

 trict pebbles and boulders of mountain limestone as the principal 

 ingredient, associated with others of old red sandstone and 

 quartz. These beds have evidently been originally accumulated 

 round the bases of the older chain in the form of coarse gravel, 

 and afford a proof of the convulsions, they must have undergone 

 antecedently to the deposition of the more recent strata. The 

 cement of these conglomerates is almost always calcareous, and 

 often consists of magnesian carbonate of lime. From the gradual 

 disappearance of the pebbles in portions of these beds, they 

 frequently pass into an homogeneous magnesian limestone 

 entirely agreeing in character, as well as geological position, 

 with the magnesian limestone in the north-east counties of 

 England. These conglomerates are often metalliferous, contain- 

 ing galena and calamine, and form the country of some of the 

 principal mines of Mendip. These beds graduate into those of 

 No. 2 ; they are considered as subordinate to it, and both are 

 included under the same general formation. 



No. 2, beds of tender red and variegated sandstone and marl ; 

 these are considered as composing, toaether with the preceding, 

 the newer redstoue formation, tlie conglomerates occurring in the 

 lower, the sandstones in the middle, and the marls in the upper 

 part of the series. The sandstones and marls contam gypsunj 

 and sulphate of strontian in nodules and veins. 



Upon this newer sandstone reposes the welUknown formation 

 of lias. The compact earthy limestones so denominated occupy 

 a thickness of about .30 feet, being covered l>y about 160 feet vf 

 blue marl, alternatinii' with a few thin seams of nnu'ly liuiestone. 

 The white has, which affords slabs proper for the purposes of 

 litliography, occupies the lowest place in the series. Above the 

 lias commences the series of oolites. No. 4, the members of which 

 occur in the folU)\ving order: 1, sandstone, with calcareous 

 concretions ; 2, the interior oolite, a coarse oolitic freestone j 

 3, clay and iuUer's-earth ; 4, the great oolite, which crowns the 

 whole escarpment ij-nd elevated platfiirm of the Cotswolcl hills, 

 and their prolongation in Somersetshire and Wiltshire. 



The edge of this escarpment is i'urrowed by deep valleys, 

 frequently cutting thruugli and exposing in section all the strat* 



