Horace B. Woodicard — On Landscape Marble. 113 



during the consolidation of the stone, and more particularly by the 

 shrinking of its upper portions. In this way, and while the mud 

 was still in a more or less pasty condition, one or more of the dark 

 films in the banded mass were disarranged and. dispersed in 

 arborescent form in the slowly setting rock. The features dis- 

 played in different specimens of the Landscape Marble suggest 

 that sometimes an upper and sometimes a lower film of dark mud 

 was dispersed. There are specimens likewise that exhibit a double 

 landscape, one above the other. An example is figured by E. Owea 

 {op. cit. pi. i. p. 163), and similar specimens are preserved in the 

 Museum of Practical Geology. In these instances there seems 

 evidence of a prior consolidation in the rock, followed by more 

 calcareous mud, the whole ultimately coalescing to form one layer 

 of limestone. It may be that the production of the isolated masses 

 of rock with their irregular upper surfaces, was attended by some 

 pause in the deposition of sediment, and by exposure of the layer 

 to the sun's rays. There is no doubt that such circumstances took 

 place during the Ehtetic period; and the rolled lumps of contem- 

 poraneous limestone met with in the White Lias near Lyme Regis 

 and near Harbury are suggestive of such exposure during the later 

 stages of the period.^ Thin veins of calc-spar occasionally penetrate 

 the ' inferior kinds ' of Landscape Marble, and these fill cracks that 

 were perhaps the final result of consolidation : the mass of the stone 

 being sometimes found in a minutely faulted condition. 



Under the microscope the dark arborescent portions appear 

 sharply defined from the main mass of the Gotham Stone, and some 

 tiny dark portions are seen to be isolated. Mr. J. J. H. Teall, who 

 kindly examined the rock, states that it is " mainly composed of 

 extremely fine granular calcite, and that it contains a few very 

 small grains of quartz. In the part which shows the characteristic 

 markings there are patches of clear and sometimes coarse-grained 

 crystalline calcite." These facts are not inconsistent with the view 

 that the appeai^ances are due to the partial intermixing of the dark 

 and light layers of mud during consolidation, albeit attended by 

 some crystallization of calcite. 



The evidence here brought forward is essentially stratigraphical ; 

 but if the suggested explanation be true, it serves to indicate the 

 kind of re-arrangement that may take place when a pasty sedimentary 

 mass solidifies in a somewhat irregular manner. 



It has been noticed that the upper surface of the Gotham Stone 

 is generally corrugated, but that it is sometimes formed of branching 

 or interlacing ridges. These latter may be connected with phenomena 

 of segregation. The segregation and concentration of calcareous 

 material is shown in the irregular and nodular character of some 

 of the Lias limestones, and in other formations where cement-stones 

 and septaria occur. Some nodules of " race " and ironstone exhibit 

 mammillated surfaces, when there is no evidence of concretionary 

 action such as would be indicated by the deposition of successive 

 coats of mineral matter. 



1 Proc. Geol. Assoc, vol. xi. p. xxx. 



DECADE III. VOL. IX. — NO. III. 8 



