vi INTRODUCTION. 



probably the Freshwater equivalents to the Crag Periods ; the first three mentioned 

 localities belonging, perhaps, to the Red Crag Period, while the Copford deposit 

 may be of a more modern date. As these localities contain Mollusca, of which all 

 the species are identical with existing forms, and which have been already figured 

 and described, it is presumed that a name alone, with reference to the work in which 

 each species is given, will be sufficient for geological purposes. The land and 

 Freshwater shells delineated here, having been found in the Red and Mammaliferous 

 deposits, intermixed with Marine species, may be considered as forming an integral 

 portion of these beds, as their geological age cannot be doubted: they therefore 

 cannot well be omitted, more especially as they exhibit, in most instances, a variation 

 in form, more or less considerable, from their typical characters, thus exciting our 

 interest regarding the climatal and other conditions under which they existed, and 

 which appear to have exerted no little influence upon most of the animals of that 

 Period. 



In justice to my predecessors in this field of geological and palseontological 

 research, a small space may be allotted for a brief summary of their labours. 



' An Attempt towards a Natural History of Fossils,' by John Woodward, in 1729, 

 contains the first notice of any organic remains from the Crag Formation. 



Robert Dale, in his ' History and Antiquities of Harwich,' published in 1 730, 

 gives copious descriptions, as well as representations, of several species from the Crag, 

 that were found at that time in the Cliff near Harwich ; the execution of some of 

 these figures is by no means to be despised, and the shells may be readily recognised. 

 This author states that during the time he had observed the Cliff, the wearing away 

 of its materials was so rapid, that after a period of forty years but little of the stratum 

 remained ft-om which he had, in the early part of his life, collected his fossils ; and 

 although portions of the Crag were remaining during the time of his publication, all 

 vestiges of it have long disappeared from that locality. 



Parkinson, in his 'Organic Remains of a Former World,' 1811, gives a few good 

 figures of Crag shells. 



In 1816, William Smith, "the Father of Geological Science in England," published 

 a plate of good figures of Crag fossils in his ' Strata Identified by Organized Fossils.' 



