IS 1 4.] MlneraJogkal Olscrvaticms. 421 



the sand-stone, are observed projecting from the strata where the 

 rock> have been much exposed to the action of the weather. Masses 

 of this kind at first sight appear to be fragments of lime-stone; but 

 I satisfied myself that such of them as I had an opportunity of 

 examining are of cotemporaneous formation with the sand-stone, 

 because they exhibit appearances similar to those presented by 

 granite in gneiss and goeuE in granite. This calcareous saud-stone 

 is met with i.t East Lothian. 



6. The same bed of sand-stone occasionally varies much in colour 

 and hardness ; thus one part of it will be red, and rather soft, 

 serving as a basis in which white and harder portions are contained; 

 or the general mass of the bed will be white and soft, and include 

 harder masses of a red variety. These included portions, like the 

 masses of granite in gneiss, vary in shape, being round, oval, 

 angular, with projecting arms like veins ; and they have either the 

 same simple granular structure with the sand-stone in which they 

 are contained, or they have a granular structure, and the sand-stone 

 in which they are contained a slaty structure ; thus affording an 

 example in sand-stone of an analogous appearance to that observed 

 in gneiss when it includes cotemporaneous portions of granite. We 

 may mention the sand-stpne of Arran and of East Lothian as afford- 

 ing instances of the appearances just described. 



7. In strata of sand-stone, as in those belonging to the first floetz 

 or old red sand-stone, and the coal formation, we sometimes meet 

 with imbedded portions of porphyry, amygdaloid, basalt, green- 

 stone, and trap tuff. These vary in shape and magnitude, and are 

 to be observed passing imperceptibly into the surrounding sand- 

 stone ; thus showing that they are cotemporaneous, not fragmented 

 masses. When the imbedded trap rocks are very compact, and the 

 sand-stone comparatively loose in its texture, it sometimes happens, 

 particularly on sea coasts, that the softer sand- stone is partly carried 

 away, and the harder, or trap rocks, appear rising through the 

 sand-stone, just as we observe harder sand-stone rising through 

 softer, a granite through gneiss, and might be confounded with the 

 outgoing or crop of a vein, or some other repository. There are 

 examples of this appearance in different places on the sea coast of 

 Scotland. 



S. The slate-clay of the coal formation, as well as that which 

 occurs in the old red sand-stone, occasionally alternates with beds 

 of green-stone, and sometimes it contains imbedded portions of 

 that rock. These portions have all the marks of cotemporaneous 

 formation, and therefore bear the same relation to the slate-clay in 

 which they are contained as the granite masses already mentioned 

 bear to tin- i.Niei^s. There is an example of this appearance near 

 Aberdour, in Fyfcshirc. 



'J. In the old red sand-stone of the middle division of Scotland,* 



• The in'nl II'- ilMrirt includes that part ftf Scotland which h) Contained lietw>rii 



it"- Firth oi Forth and the chain of Lakei extending from Inrenea to l-'ort 

 \\ Lilian. 



