324 Mr. Weaver's Geological Observations on 



particular on the planes of separation, (as is also the case with the sandstone,) 

 partially silvering over their surface. When the slate-clay occurs in the vicinity 

 of sandstone, it is often intermingled with sandy particles, and when contiguous 

 to limestone with carbonate of lime ; in both of which cases it acquires 

 a firmer consistence and compacter structure. Sometimes also it contains 

 interrupted layers and portions of sandstone and carbonate of hme, parallel to 

 its laminaB. 



The structure of the transition limestone varies from the perfectly compact 

 to the foliated granular ; and its predominating colour is gray ; but it is also 

 casually tinged with red or green, when adjacent to sandstone or slate-clay ; 

 and in these cases it is sometimes intermingled with sandy particles, or clayey 

 matter, and envelopes unconnected layers and portions of those substances. 

 It not unfrequently occurs also of a magnesian quality, being then generally 

 of a yellowish or reddish gray cast, and minute foliated granular structure. 



These transition beds are often traversed by slight veins and filaments of 

 calcareous spar, and brown-spar ; and occasionally also, though much more 

 rarely, are to be observed interrupted layers and veins, and disseminated 

 portions of sulphate of strontian, as well as of sulphate of barytes, all of 

 which bear evidence of a contemporaneous origin. 



The sandstone, limestone, and slate-clay, are frequently associated with 

 layers of soft, reddish, blueish, or greenish clay, and also with blueish and 

 greenish white marl, the whole series being found in beds of variable thick- 

 ness, interstratified with each other. The prevalence of any one member 

 varies in different parts ; but in general it may be said that the sandstone 

 predominates in the lower, and the limestone in the upper portions of the 

 series. 



The trap is of very variable character in different quarters ; consisting 

 of granular and compact greenstone, (the former seldom appearing of a di- 

 stinctly crystallized structure,) with occasionally disseminated portions of horn- 

 blende or augite, sometimes, though very rarely, graduating into basalt ; of 

 granular and compact felspar ; of clay-stone, and amygdaloid ; all of which, 

 being mutually intermixed, frequently interchange characters and pass into 

 each other; and hence the shades of colour are never constant in any con- 

 siderable portion of the mass, but fluctuate from black, to green, red, brown, 

 and gray, the predominant colours being reddish brown, and gray. The 

 rock sometimes also, though very seldom, assumes a porphyritic appearance, 

 thinly scattered acicular crystals of glassy felspar occurring in its substance. 

 But in general the common aspect of the trap may be said to be that of a 

 compact rather than of a crystalline or even sub-crystalline production ; and 

 where steatitic matter prevails, it is of a loose consistence, friable and earthy. 



