On the Pkosphoric Strata of the Chalk Furmation. 
63 
in its relation to the object of the present paper, as at its junction 
with the gault it constantly discloses a bed of fossils in large 
quantities, in which phosphate of lime forms the chief ingredient. 
Other portions too, in some localities, contain bands of fossils 
which are rich in this substance. To the upper bed, however, 
most importance is attached, on account of the singular persistence 
of similar phosphatic deposits below the whole range of the 
gault. 
The preceding brief general description of . the strata involved 
in this narrative will probably not be found minutely applicable 
to every neighbourhood, but it is believed to be correct in its 
main features, and will serve to indicate the localities in which 
phosphoric remains are likely to be discovered in the vicinity of 
the chalk. With these preliminary observations it may be well 
to proceed to detail such particulars relative to the discovery, 
exact position, and practical application of the phosphatic strata 
of the whole cretaceous system, as have been noticed by the 
authors, or recorded by other observers. In the necessarily 
hurried examination of the works of geological writers, it is 
probable that some things may have been overlooked which are 
pertinent to the object in view ; and some works in which allu- 
sions may have been made to this subject possibly have not been 
referred to at all. In either of these cases an apology is offered, 
it being an intention most remote from the wishes of the writers 
to withhold from previous observers their due meed of merit, or 
to approj.riate to themselves without acknowledgment the labours 
of others. 
Reverting to the first subdivision of the upper green-sand, or 
zone of fossiliferous green-marl, the position and thickness of 
which have been noticed above, it may be advisable here further 
to observe that the greenest marl is not always the richest, but, 
on the contrary, that which is intermixed with calcareous matter 
of a white and brown colour affords the largest percentage of 
phosphoric acid. The fossils which are enveloped in the marl 
are by no means evenly dispersed through the bulk, but often lie 
in most irregular heaps. In this respect, indeed, as well as in 
the thickness of the deposit, there seems to be no approach to 
uniformity. Frequently, however, as will be hereafter shown, 
the fossils are found in great abundance, and their principal con- 
stituent is phosphate of lime. These organic remains comprise a 
great variety of zoophytes, many shells, echini, ammonites, fishes' 
teeth, and wood. A large proportional ingredient of the marl 
itself, when separated from the fossils, is also phosphate of lime, 
containing frequently from 10 to 15 per cent., and in some in- 
stances even more. 
On referring to the geological map, we may trace the line of upper 
