34 



aspect was given to the region, most probably that of a wide archi- 

 pelago, in whose winding channels and on its little elevated lands, 

 was formed a new series of alternating marine and fresh-water 

 strata, almost a repetition of those far down in the series. To ex- 

 plain the origin of the upper portion of the marine series, the thick 

 body of strata ranging north of Glasgow and across the higher 

 portions of the city, we must again suppose the existence of a sea 

 of considerable depth, receiving an abundant and very mixed sedi- 

 ment, and the waste of a prolific land vegetation of a tropical or 

 sub -tropical character. The close of this period was marked by the 

 elevation of large tracts along the margins of the area, and the 

 formation of a lake or estuary filling the central and depressed 

 portion, now occupied by the upper or fresh-water coal series already 

 described in Art. 17. The climate remained unchanged, and the 

 vegetation then attained its maximum of development, resembling 

 more that of a tropical jungle or river-delta, than anything now seen 

 in our latitudes. Then began that remarkable series of changes in 

 repeated depressions and elevations of the bottom and margins of 

 this lake or estuary, which geologists have often attempted to 

 chronicle, in describing the physical geography of the coal period. 

 These are much the same in Clydesdale as in other coal tracts, and 

 we need not here attempt the description. We may observe, how- 

 ever, that the underclay, or floor of the coal, generally exists in our 

 fields, roots being often seen passing down through it ; and that 

 ranges of upright trees have been met with at several levels amid 

 our coal measures. These underclay s and seats of the trees point 

 out the successive surfaces on which the vegetation flourished, and 

 which, though perhaps slightly depressed, cannot have been far 

 below water ; the coal seams are a sort of rude chronometer indi- 

 cating the time occupied in the deposit, while the interposed sand- 

 stones and shales show the amount of depression which took place 

 before the surface was again fitted for the growth of plants. This 

 series of changes was continued through vast periods of time, till 

 at length the rich storehouse was furnished with those materials 

 which were destined, in the providence of the Creator's goodness, 

 to contribute to the wants and happiness of Man, when he should 

 be called into being upon that theatre, already the scene of the 

 creation and extinction of many races which had served their 

 purpose and disappeared. But the series of revolutions was not 

 yet completed. The entire area, with portions of its borders, was 

 again submerged to a depth probably exceeding 300 fathoms ; the 

 strata were fractured and dislocated in all directions, and successive 



