BALDERSTON : THE SILURIAN ROCKS OF INGLETON. 141 



situation, converge towards the same point, (iv) In the Skirwith 

 fields, N. to N.E., are nine exposures, most of which are 4 ft. or 

 more in width ; those to the S.E. are very sound, and of a paler, 

 smoky to silver-grey colour, of great hardness, and considerable 

 compactness ; here, too, the dyke bifurcates into two parallel 

 branches. This dyke approaches kersantite and the darker or less 

 acid division of the Helmsgill traps, and is not unlike No. 5. 

 Constituents : orthoclase, red and pale nests ; hornblende, green, 

 minute ; mica, black, pale green and silvery ; calcspar, substitution 

 products of red orthoclase in some situations. Extreme points of 

 exposure, 1^ miles. 



No. 9. — The Green Cross Dyke Series. Eleven or twelve 

 exposures of the four main dykes, with several belonging to minor 

 branches; 180 ft. of green galliards intervene between (i) at the 

 point a little above the Breast Springs Foss and dyke No. 8. 

 (i) 5 ft. to ih ft. wide; five principal exposures, that showing the 

 finest section running at a strong angle across the bedding, and 

 coming obliquely from a high breast of slate in the upper quarries 

 of the Doe belonging to Group 5 of the stratified series ; here it is 

 regularly jointed, nearly horizontally, into large cubical blocks, the 

 joints being occupied by thick bands (mainly quartz, but with a little 

 felspar, calcite and chloritic matter), which die away quickly in 

 fusiform extensions in the slate on each side, (ii) 4 ft. to 2 ft. wide, 

 seen best a few feet from (i), close to the river Doe, at a point a little 

 below the quarry, and, perhaps, more notable for reddish-brown iron 

 decomposition products. Both these dykes rise alongside each 

 other to a great height, gradually approximating as they get nearer 

 the top of the rocks to the S.E. of the river, (iii) About 150 ft. 

 above the quarries another band crosses the river, (iv) 210 ft. further 

 a fourth dyke of the same series may be seen in a gully on the N.W. 

 side of the river ; this also is crossed by parallel but oblique bands 

 of quartz, and thus regularly jointed. Besides the foregoing, there 

 are several thin branches, and the whole may be regarded as one 

 series springing from a double central dyke, running strongly across 

 the bedding, and giving off branches in a plumose manner aiong the 

 lines of stratification. There are slight variations in compactness, 

 amount of substitution products, porphyritic calcspar, apatite, rusty 

 stains and chloritic matter. The rock is much altered everywhere, 

 and its shrinkage blocks and green colouring matter are prominent 

 features. Its constituents are : hornblende, green ; quartz, not 

 unfrequently porphyritic, or as a substitution product in some 

 places ; calcspar ; apatite, clusters ; ferrous and chloritic products ; 

 micaceous matter, black and altered ; felspars, probably triclinic. 



May 18S9. 



