Great Valley of the Scottish Lowlands. 111 
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- 
