12 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NoV. 2, 



faces, sun-cracked surfaces, appearances resembling rain-marks, rep- 

 tilian footprints, and the frequent conversion of these sandstones and 

 of the clays resting immediately upon them into ancient swamp-soils. 

 Few of the beds attain any considerable thickness without alternating 

 with shales. The thickest continuous bed in the section is that at 

 Coal Mine Point (Group XVI.). There are, however, much thicker 

 beds in the upper and lower parts of the measures, beyond the limits 

 of our section. 



Evidences of contemporaneous currents and denudation are very 

 frequent. On the lower surfaces of some beds resting on clay there 

 are casts of scratches and furrows, as if produced by drift-wood with 

 branches swept over the surface. In the case of beds which contain 

 great numbers of trees retaining their bark and markings, and con- 

 fusedly disposed, we may fairly infer that these have been swept 

 away from forests invaded by the sand-bearing currents. The bare 

 coniferous trunks found in other beds may have been long drifted 

 in the sea. In other instances, the occurrence of numerous trunks 

 and fragments of trees, covered with shells of Spirorbis, testifies at 

 once to drift and to mtermissions of deposition. We may account 

 for the imbedding of so many plants in the erect position by allowing 

 for their strength and toughness when recent, and for the resistance 

 presented by the matted soils in which their roots were imbedded. 

 It is worthy of remark, however, that in the two best-preserved beds 

 of Calamites, as well as in several cases of tlie occurrence of erect 

 trunks, the lower parts of the stems were imbedded in mud or very 

 fine sand, and were thus strengthened and protected before coarser 

 sand was swept over them * . 



Well-marked instances of irregular denuding action are afforded 



Fig. 1. — Section of Sandstones and Shales in Group XIX., showing 

 denudation and filling up. 



a, a. Sandstones. 



a'. Sandstone with drift-wood. 



b. Shales. 



by the clays and sand-beds cut off by coarse sandstone represented 

 in figs. 1 MS., 2 MS. (fig. 1), and 1 A, ms., which are the best in- 



* This is also the case in the bed with erect Calamites near Picton, Quait. 

 Jouru. Geol. Soc. vol. vii. p. 195, fig. 1. 



