29 



stone in the West of Scotland. The following section shows the 

 order and thickness of the strata : 



Feet. Feet. 



1. Surface soil, . 16. Coal, . * ... .1 



14 7. Slate clay, . . . .6 



2. Limestone, full of marine fossils, 



3. Fire clay, .... 



4. Limestone, .... 



5. Clay indurated, . 



Limestone, with few fossils, . 18 



9. Coal, 1 



10. Slate clay, not passed through, ? 



The strata are traceable for a mile in the line of bearing, but the 

 breadth is limited in the direction of the dip. They crop out towards 

 the north in the direction of the great outburst of trap, already 

 noticed as forming a mineral axis in this region, in connection with 

 the old red sandstone, through which it has been erupted. 



23. On the subject of these local variations, and the prevailing 

 similarity among the local groups, Mr. Montgomery of Cloak has the 

 following remarks respecting the fields of Kenfrew and North Ayr, 

 in his clear and accurate outline of the geology of these tracts :* 

 " The different strata alternate in no definite order, while no one of 

 them seems essentially necessary to the formation of a coal field. 

 Even coal itself may be awanting, whilst all the other strata 

 usually found in a coal basin are there. The place usually occupied 

 by freestone or slate clay is occasionally filled by ironstone. Lime- 

 stone is as capricious in its presence or absence as any other of the 

 measures ; nor is it possible even to define its limits in the district 

 under consideration. It makes its appearance here and there, more 

 particularly upon the edges of the coal fields ; but its continuity from 

 one place to another where it is seen is by no means certain. In 

 various places it has been wrought out, perhaps indicating that the 

 quarries had been opened in masses detached by some convulsion 

 from greater strata. But whatever hypothesis may be adopted re- 

 garding this matter, none favourable to the opinion of the limestone 

 strata holding a necessary place in the coal measures of Renfrew and 

 Ayr can be entertained. If the strata of limestone were ever con- 

 tinuous, they certainly are not so now ; and to support the opinion 

 of their former continuity, a much more intimate acquaintance with 

 their numerous organic remains would be necessary, than it is sup- 

 posed that any one has yet acquired." 



24. We do not know that these remarks, penned twenty years ago, 

 need any modification at the present time, with all the knowledge 

 we have since acquired respecting the organic remains of these beds. 

 They support the opinion already advanced, upon evidence furnished 

 by other districts of our great coal tract, that there is no great 

 persistent body of "carboniferous limestone" separating by a well 

 marked horizon the "upper" from the "lower" coal measures, and 



* Jour. ofAgricul. and Trans, of Highland Soc., vol. xliii., p. 441, 1839. 



