GENERAL CONSIDERATIONS. 7 



slow meteorological influences, namely, by the gradual action of air, moisture, carbonic 

 acid, alternations of temperature and the like, through long periods of time. So that in the 

 absence of fossiliferous clays of marine origin, which in later geological formations are the 

 most productive source of Foraminifera, recourse may be had to those particular portions of 

 the limestone strata in which partial disintegration has been brought about by the means 

 alluded to. Thus, the decomposed friable layer, which is often found overlying the hard 

 rock, and between it and the superficial soil, may often be examined with advantage. 

 The marly partings between the scams of limestone, weathered calcareous shales, or the 

 thin earthy plates, such as arc occasionally found interbedded with compactor rocks, yield 

 similar valuable material. At best the sources of Foraminifera are very uncertain, and 

 in the majority of cases, after much washing, drying and sifting, the result is nothing 

 beyond a little grey heap consisting of the di-bris of Encrinites, Polyzoa, occasional 

 molluscan Shells, and a few Entomostraca. Frequently, especially in the neighbourhood 

 of ironstone deposits, the fossils, especially the minuter ones, are so corroded as to be 

 identified with difficulty. But notwithstanding the large proportion of examinations that 

 must be made with nothing but negative results, there is still a residuum sufficiently 

 productive and interesting to reward the collector. 



The method of the following pages has been determined by the conditions under 

 which subject is approached. Clean specimens free from the matrix have been 

 employed, as far as practicable, as the basis of description, both of external characters 

 and internal structure ; the principal, if not the only, exceptions being in the case by some 

 two or three species accepted on the authority of other observers, in which there has been 

 no available means of verification. In addition to the figures of external form, drawings of 

 sections of individual Foraminifera have been as far as possible introduced with the 

 object, primarily, of illustrating the structural features of each species, but also to 

 facilitate their recognition as they present themselves in sections of hard limestones. 

 With the exception of some half dozen figures of Permian specimens, which are in each 

 case marked as " copied," the whole of the figures in the accompanying plates have been 

 drawn direct from nature, and they represent actual specimens with all their im- 

 perfections, as they are, not what they may have been. They were for the most part 

 originally drawn by myself, but practically they have been redrawn in their transfer to 

 the stone by my friend Mr. A. T. Hollick. The fidelity of Mr. Rollick's work is now 

 too well known to need commendation from me ; and I have only to express my thanks to 

 him for the care and pains which, in spite of considerable difficulties, have ensured results 

 so satisfactory. 



