58 On the Phosphoric Strata of the Chalk Formation. 
time to time been directed to the inquiry, whether there existed 
any available source of phosphate of lime capable of furnishing 
this mineral for the use of the farmer at a cheaper rate than he 
obtains it in bones, or adequate to replace them if their supplies 
should fail. 
It is needless to advert, except in the most cursory way, to 
guano, which is chiefly valuable for the ammonia and phosphate 
of lime contained in it. The Peruvian guanos certainly owe 
their greatest efficacy to the large proportion of ammoniacal salts 
which they contain ; but some other kinds (as the Saldanha Bay 
guano) must be considered in the main as vehicles for phosphoric 
acid. 
In the year 1843 Dr. Daubeny undertook a geological expe- 
dition to the province of Estremadura in Spain, for the purpose 
of inspecting a bed of phosphate of lime which was said to occur 
in that district, but concerning which only the most vague and 
unsatisfactory information was at that time possessed. 
Dr. Daubeny's account of this phosphoric bed is in the highest, 
degree interesting ; but although very large quantities of the 
mineral were to be obtained, he came to the conclusion that at 
present, at all events, it was not likely to become available for 
the purposes of English agriculture. For the history of this 
mineral the reader is referred to the Journal of the Agricultural 
Society, vol. v. part ii. ; but it may be well, for comparison sake, 
to mention here that the quantity of phosphoric acid found by 
Dr. Daubeny in the purest specimens was about 37 per cent., a 
quantity which would be equal to about 76 per cent, of the bone- 
earth phosphate.* 
More recently the very important discovery was made by 
Professor Henslow that certain rounded waterworn nodules exist- 
ing in the crag and London-clay formations contained a large 
per-centage of phosphate of lime. From the form and external 
markings of these singular concretions, taken with the fact that 
the teeth of sharks and other organic remains were frequently 
found in the interior of the lumps, Professor Henslow was at 
that time led to conclude that they were the fossil dung of a 
former generation of animals, and proposed for them the name 
of cojjrolites, by which they have since then been known. 
Further observations have induced the discoverer of these 
fossils to modify very considerably the views which he at that 
time entertained of their origin, but the name is convenient, and 
* Note by Mr. Way. — Dr. Daubeny considers the phosphate of lime in 
this mineral to be the tribasic phosphate (3CaO PO5), which contains 
45*5 per cent, of phosphoric acids. He found 81 per cent, of this 
phosphate in the substance ; and from these data the numbers above are 
deducible. 
