S*7<) Mr. Horner on the Geology of the 



inch' or two in thickness, gradually thins away at each extremity, 

 sometimes to a hair's breadth, at other times shooting off like a 

 spreading root of delicate fibres. Very often a slender thread cuts 

 across a thick vein, throwing it several inches out of its regular 

 course, affording a miniature representation of the disturbances in 

 the great veins of mining districts. These veins do not penetrate 

 the slate either above or below the stratum of limestone in which 

 they are contained : but there are other veins of calcareous spar 

 which cut through the strata, generally occasioning a dislocation, 

 and in many instances I observed the substance of the vein pene- 

 trating the adjoining strata in minute ramifications. It will be diffi- 

 cult to reconcile these appearances to any theory, of veins that has 

 yet been proposed ; like other instances, which every country 

 affords, they tell us how little we yet know of the laws by which 

 the materials of our globe have been brought together into their 

 present arrangement. 



§ 38. The slate clay that is interposed between the strata of 

 limestone assumes different appearances. In some places it is grey, 

 in others brown, and in others nearly black : it is frequently bitu- 

 minous, having, when broken, a strong fetid smell. The strata 

 are divisible into laminse as thin as common pasteboard, splitting 

 ■with the greaitest facility, and where it is washed by the sea it is 

 very soft arid friable. It appears to contain the same fossils as the 

 limestone, and it is in this that the flattened ammonites are fourjd ; 

 those in the limestone preserving their natural form, as far as my 

 observations went. It frequently contains imbedded masses of a 

 limestone identical with that of the regular strata, of a lenticular 

 shape similar in form to the masses of clay-ironstone found in the 

 clay of the coal formations. ; These are frequently uniform in 

 structure throughout, sometimes they, contain slender veins ofcal- 



