80 Prof. Sedgwick on the Carboniferous Chain 



succession of tabular hills ; in others^ it forms a terrace on the sides of the 

 mountains terminating a succession of green pastures, which rise in inter- 

 rupted slopes from the neighbouring valleys. Above it the strata often lie 

 concealed under accumulations of black turf bog ; and the highest summits of 

 the mountains terminate in great irregular masses of tabular millstone grit. 

 Near the line of section its greatest thickness is about eighty feet ; but in one 

 or two places it thins off and almost comes to an edge ; and its average thick- 

 ness is under twelve fathoms. 



The mineral characters of the group are so nearly the same with those of 

 the four -fathom limestone, that the same description may almost serve for both. 

 Its prevailing colours are grey, and some of the beds exactly resemble ordinary 

 specimens of the great scar limestone. Most commonly this group is distin- 

 guished by the abundance of encrinital stems, which in some rare instances 

 so nearly constitute the whole mass of the strata, that the cementing principle 

 is almost wanting, and the weathered surfaces of the blocks rapidly disinte- 

 grate and fall into innumerable cylindrical fragments*. In general, however, 

 the encrinital fragments are held firmly together by a grey, subcrystalline, cal- 

 careous cement, and form hard beds, the most regular of which admit of a 

 good polish. The most beautiful variety of this fossil marble, is obtained from 

 one or two of the upper beds of this group, and is quarried at Snays-wold Fell, 

 between Dent and Garsdale. The dull grey base in which the fossils are 

 commonly imbedded, is there enlivened by many dark cloudy blotches, arising 

 out of the irregular distribution of the colouring bituminous matter. The 

 group appears to terminate in a few, thin, impure beds of dark bluish lime- 

 stone alternating with slaty gritstone and carbonaceous shale f. 



So far the relations of the successive groups may be ascertained with a near 



* Beds of this kind burn to a pure lime very readily : but on extracting it from the kilns, in- 

 stead of coming out in such lumps as are convenient for transport, the lime frequently falls at once 

 into a fine impalpable powder. Some beds of this kind overlie the coal-seam (No. 10(6.)) at a 

 hill called The Cross in the valley of Dent. 



f Section of the marble quarry of Snays-wold Fell, in the descending order; — 



Feet. Inches. 



5. Hard, dark blue limestone, and a 



Feet. Inches. 



1 . Carbonaceous shale 4 



2. Flaggy, brown grit 1 



3. Hard, dark blue, impure limestone 2 4 



4. Shale and gritstone irregularly mix- 



ed together, and containing much 

 calcareous matter in nodular 

 masses, with large stems of En- 

 crinites 10 



thin band of shale 1 6 



6. Fine, compact bed, with crystalline 



stems of Encrinites 1 10 



7. Shattered beds and shale 6 



8. Strong Encrinite bed 3 



9. Lower calcareous bed, not exposed 



in the section. 



Nos. C. and 8. are the only beds used in the marble works. 



