46 



THE GEOLOGIST. 



another condition under which bitumen was eliminated. In this case 

 it is the result not of mechanical deposition, but of subsequent chemi- 

 cal action from decaying organic substances. Again, the action of 

 the currents was resumed, and fresh bituminous shales were formed. 



When the contemporaneous traps on the north-west side of our 

 section were ejected, the same succession of physical changes con- 

 tinued. Bitumen occurs in globules both in the contemporaneous 

 traps and in the limestones. The limestones indicate three marked 

 alterations in the level of the land. Eirst, the Kirkton limestone, 

 with its leafy laminae, and curiously baked beds of cherty porcelain, its 

 interstratified ash, and over-capping basalt indicate proximate vol- 

 canic activity when forming. Eluvio-marine fossils are found in it. 

 The laud then sank so far as to allow the building corals to com- 

 mence their labours ; a reef was now formed w^hich was added to by 

 shells dashed in by the surf from the neighbouring sea, and the pre- 

 cipitation of carbonate of lime from a sea surcharged from its prox- 

 imity to a volcanic cone ; thus the great belt of the limestone of the 

 hills was formed. But immediately after the land was subject to as 

 rapid an elevation ; as is manifest from the Stigmarias found in the 

 upper bed of the limestone, — the lower beds abounding in deep-sea 

 shells. Ash-beds also cover it. The hills now seem gradually to 

 have risen above the waves, and a prevalence of freshwater strata 

 filled the small Torbane Hill basin. But all this time the volcano did 

 not stop its activity, as is evidenced by the thick ridges of inter- 

 bedded basalt whicii may be traced terracing the country upwards 

 from Bathgate. It is easy to suppose that sheets of bitumen, as at 

 the prior period of the Binny sandstone, floated ou the waters of this 

 lagoon ; that in one time in particular, a very large quantity was 

 given out, and thus, aided mayhap by ejections from beneath, the Tor- 

 bane Hill bed was formed. May not the round circular masses in the 

 Torbane Hill mineral, w^hich so puzzle microscopists, be the result of 

 the action of currents, — only, however, on a smaller scale than those 

 visible to the naked eye in the other rocks of the district ? In sug- 

 gesting this hypothesis we make allowance for the fact that at other 

 tunes the basin was elevated so that morasses could accumulate, and 

 thus the beds of coal be formed. The district thus exhibits evidence 

 of both modes of the elimination of bitumen. 



In the upland country west of the Torbane Hill basin there is a sin- 

 gular absence of trappean ridges. The district rises into a series of 

 undulating hills formed solely of the upper members of the carboni- 

 ferous system of Lanarkshire. The lower carboniferous volcano had 

 ceased previous to their deposition ; and the Bathgate bills probably 

 formed elevated land at the base of the great strait in which these 

 strata were depositing. Slowly the land rose and fell, morass after 

 morass accumulated to be compressed into future coal-beds after being 

 covered over by sand and mud. Bitumen was thus formed through 

 chemical agencies. Its source is manifest from the microscopic struc- 

 ture of the coal, which is entirely of Avoody origin, not exhibiting 

 traces of clay or sand from drift. The beds of this upper formation 



