THEIR ROCK-SYSTEMS. 191 



Western Europe, for it must be observed that in India, 

 Eastern Europe, in Farther Asia, and Southern Africa, as 

 well as in various tracts of North America, the conditions 

 of deposit seem to have been widely different, as there 

 both oolitic and cretaceous coal-fields are by no means 

 uncommon. And these coals, as noticed in a former 

 sketch (Coals and Coal - Formations), must have been 

 formed, like all others, partly from vegetation that grew 

 and accumulated in situ, and partly from drifts and rafts 

 borne down by rivers during seasons of flood and inun- 

 dation. 



There is thus nothing very puzzling in the lithology or 

 mere rock-formations of the secondary ages. In the sand- 

 stones of the Trias studded with footprints and rain- 

 prints, and reticulated with sun-cracks, we see the sandy 

 deposits of shallow shores; in the shelly limestones, the 

 accumulations of somewhat deeper waters; and in the 

 clayey marls, with their masses of rock-salt and gypsum, 

 the muds of lagoons and sea-creeks alternately submerged 

 and cut off from communication with the outer waters. 

 In the limestones and calcareous clays of the Lias and 

 Oolite, we perceive the coral-growths and organic debris of 

 exterior seas ; in their freestones and shell-beds, the drifts 

 of the nearer shore ; while in their coals and jets we dis- 

 cover the growths of sea-swamps and deltas, and the drifts 

 of streams and rivers. Again, in the greensands of the 

 Chalk we trace the operations of the more exposed shores ; 

 while in the Chalk itself we perceive the slowly-accumu- 

 lated calcareous ooze of the quieter waters. For just as in 

 the Atlantic and other sea-beds, the fine calcareous mud 

 resulting from organic debris (the shields of foraminifera, 

 the waste of corals and shells and other exuvise) is now 

 collecting in great thickness and purity over extensive 

 areas, so in the older cretaceous ocean similar agencies were 



