

SKY. GEOLOGY. SECONDARY STRATA. 319 



In examining the two ends of the principal limestone 

 tract, the one near Swishnish and the other near Broad- 

 ford, differences will be found in the relative number 

 of the calcareous beds compared to those of shale and 

 sandstone, the greatest proportion of the former being 

 at the place first named. This lateral variation in the 

 course of one bed, or of any particular set of beds, is 

 however so common as to render any further notice of 

 it unnecessary. 



Where the limestone first occurs on the north-eastern 

 side of the island at Lucy, it is found dipping at the 

 very low angle of 5 to the north-west ; following,, at 

 the small and interrupted interval formerly noticed, the 

 sandstone, which has here subsided from its usual high 

 angles to one of 10. It alternates here with beds of 



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a brown argillo-calcareous sandstone, and, in further 

 progress, with a shale which in many places becomes so 

 predominant as altogether to exclude the calcareous 

 rock. This shale is of a very compound nature, con- 

 sisting of blue clay mixed with sand, mica, and calcareous 

 matter ; in some places also containing rounded balls of 

 trap. It is tender and irregularly fissile into thick laminae ; 

 and, like the sandstone, contains the same organic re- 

 mains that are found in the calcareous beds. The lime- 

 stone is always of a blackish blue colour, commonly fissile 

 or thinly laminar; and, although generally of an opake 

 earthy aspect, it sometimes shows a tendency to the con- 

 fused and imperfect crystalline texture so common in 

 primary limestones. In purity of composition it varies 

 extremely, since it is frequently intermixed with one or 

 other of the substances that compose the rocks associated 

 with it, namely, slaty clay, or sand. 



The organic remains are limited in variety, and very 

 irregularly dispersed ; being often absent for a long space, 

 while in other cases they are much crowded together. 

 The lowest beds seem almcfst exclusively occupied by 



