312 JURASSIC. 



The fossils of the Collyweston Slates include Pecten ptimihis, 

 Avicida Bi'aamburiejisis, Pinna cuneata, Gervilh'a acuta, Trigonia 

 compta, Pholadomya fidicula, Ceromya Bajociana, Gonioinya literata, 

 Perna rugosa, Hlodiola Sowerbya7ja, Lticina Wrightii, Myacites Scar- 

 burghensis, Pterocei-as Benfleyi, Alaria Phillipsii, etc. They do not, 

 however, yield remains of Mammals, etc., like the Stonesfield 

 Slate. The surfaces of the slates exhibit the proximity of the 

 shore, in ripple-markings, worm-tracks, and burrows, as well as by 

 numerous plant-remains. 



At Dene Brickyard the section, according to Prof. Judd, is : — 



Lincolnshire Limestone 9 feet. 



Bed with siliceous concretions (Collyweston Slate) 3 ,, 



Northampton Sands 20 ,, 



Upper Lias Clay. 



The following section" at Easton shows the succession of beds 

 from the Lincolnshire Limestone to the Northampton Sands :^ — 



Feet in. 



Oolitic limestone, sandy in places. Lincolu shire LiiJiesto7ie 12 o 



Sand with siliceous concretions 4 o 



Limestone, partially oolitic 2 6 



Indurated sand, with concretionary masses I 6 



Siliceous limestone 2 o 



Finely-laminated, calcareous sandstone beds, which weather 



into "slates" 2 O 



Hard flaggy, siliceous beds, with mammillated surfaces 



(pot-lids, etc.) o 6 



Sands 6 o 



Ironstone-beds ("Red-rock"). Northavipton Sands. 



The Collyweston Slate has been largely employed as a roofing-material, but 

 Prof. Judd observes, that excepting for ecclesiastical and other Gothic buildings, 

 and for strictly local purposes, there is now little demand for the slate. A con- 

 siderable number of pits are still worked, but over a large area the 'slate' has 

 been exhausted. The pits commence east of Collyweston, and extend to Easton. 

 The beds are quarried at those localities, and also at Dene, Kirby, and Wittering, 

 There is only a single bed of stone (the lowest hard bed of the series) which is 

 used for making tiles : this varies greatly in thickness,- — from six inches to three 

 feet, while not unfrequently the bed is absent and represented by sand. The 

 slates are worked either in open quarries or by drifts (locally called " fox-holes") 

 carried for a great distance under ground, in which the men work by the light of 

 candles. One of the deepest quarries at Collyweston showed eighteen feet six 

 inches of alternations of sand, bluestone, and slate. The slate when first raised is 

 a hard and solid stone ; on exposure to moisture and frost it becomes fissile. The 

 work of quarrying is carried on only in winter, for, if dried by the summer sun and 

 wind, the rock hardens and will not split. The holes are blocked up in spring, 

 and the quarrymen then employ their time in the preparation of tlie 'slate.' The 

 splitting is partly aided by the presence of organic remains ; but the fissile 

 character is local, as in some places the beds become worthless for roofing- 

 purposes. "Slate-mines " have been opened since the time of Henry VII. 



^ Judd, Geol. Rutland, etc., pp. 156, 1S2. See also Ibbetson and Morris, Rep. 

 Brit. Assoc. 1847, Trans, of Sections, p. 127 ; Sharp, Q. J. xxix. 243 ; V. Geol. 

 Assoc, iii. 243 ; and Phillips, Geol. Oxford, etc., p. 408. 



