Great Valley of the Scottish Lowlands. 1 1 1 



the Scottish Lowlands, forming either a strait or channel between 

 two islands, or perhaps a vast estuary into which the rivers of the 

 neighbouring primeval countries discharged their waters. The 

 ripple marks, which are so remarkably displayed on the surface 

 of the different beds of this series, even of those which are now 

 the most highly inclined, likewise afford very strong evidence in 

 favour of this supposition. 



If we examine the nature of those portions of the district re- 

 ferred to, which form the exceptions to that regularity and con- 

 tinuity of the beds of the carboniferous series, we have supposed 

 to have prevailed at the period of their deposition, we shall at 

 once see that the rocks of which they are composed ; although 

 equally formed beneath the sea, could not like them have been 

 mechanically produced by the transporting action of water, their 

 crystalline character, and the various phenomena exhibited in 

 their relations with the fossiliferous strata, affording sufficient 

 proof of their origin having been due to a different agency, as 

 well as that the ranges or groups of hills of the same description, 

 which are now seen to interrupt or cut off the coal-measures se- 

 parating them, into the fields or basins in which they are found 

 at the present day, have for the most part been elevated at pe- 

 riods subsequent to the deposition and consolidation of that 

 series. 



It is now generally admitted, that these trappean hills and 

 rocks are of igneous origin, the eruptions of porphyry, greenstone, 

 or basalt by which they were produced having taken place from 

 submarine volcanoes, or through cracks or fissures in the previ- 

 ously existing strata which at that period formed the bottom of 

 the sea, over the surface of which the igneous matter appears to 

 have been poured out in sheets of greater or less extent, either 

 continuously, that is to say, one stratum overflowing another in 

 constant succession, so as to form the immense overlying masses 

 which everywhere present themselves to view in the coal mea- 



