CARBONIFEROUS DISTRICT OF COLCHESTER AND HANTS. 26 J 



makes up whole layers of the limestone. There are also sea-mats or 

 Polyzoa^ of the genus Fenestella^ some of which spread out into leaves 

 several inches in length. 



The only shell in this limestone that appears to be identical with 

 any of the creatures whose remains are entombed in the coal measures 

 of the Joggins is the little Spirorhis, which has attached itself to the 

 inside of the outer chamber of some of the larger Nautili, after the 

 death of their owners, and this is evidently a distinct species from the 

 S. carbonarius. The reason of the difference in the fossils of these 

 different members of the same geological system is, that one is of 

 marine or deep-sea origin, while the other represents the tenants of the 

 shallow creeks, lagoons, and estuaries of the same period. A similar 

 difference subsists in all modern seas. While, however, distinct species 

 and genera of fossils occur in the littoral and oceanic deposits of the 

 same era, still more decided differences distinguish the formations of 

 one period from those of another ; for instance, the Lower Carboniferous 

 limestones from those of the older Devonian and Silurian periods. 

 Hence, if the student once familiarizes himself with the shells of the 

 Windsor limestones, or even with the species represented in the fol- 

 lowing pages, he has the means of recognising the limestones of the 

 same age in all parts of the country, and of distinguishing them from 

 those of every other formation. 



The sandstones and marls of this Windsor section differ little from 

 the similar beds in the coal measures, except that they are less lami- 

 nated, and less sorted into sand and clay, and contain no vegetable 

 remains — all indications that they were deposited in deep water at a 

 distance from land, and where changes of tides and currents had little 

 influence. The limestone is evidently the result of the growth of shells 

 and corals in the sea- bottom, forming in the course of ages thick and 

 widespread masses, like the coral reefs of the Pacific, with beds of fine 

 calcareous mud and comminuted shells and corals washed from these 

 banks or reefs by the sea. The coral and shell bank itself forms a rich 

 fossiliferous limestone. The material produced around it by the 

 wasting action of the sea becomes a compact earthy limestone, with 

 few fossils, except minute fragments of shells, often only to be detected 

 by the microscope. 



The only apparent anomaly in the deposit is the gypsum, which 

 must have been formed by chemical action, or deposited from solution 

 in water. Various explanations may be given of the origin of the 

 veins and masses of gypsuni which occur in different geological 

 formations, from the Silurian to the Tertiary, and which, so far as I 

 am aware, are peculiar to the Lower Carboniferous scries in no country 



