416 
Phosphorite in Estremadura. 
Now a portion of this soil, after having been carefully freed from all 
the loose pebbles, &c., which it contained, being taken from the portion 
■which had passed through the finest of the sieves, was carefully ex- 
amined, in order to ascertain the presence in it of phosphate of lime, 
but only the merest trace of that substance could be discovered, less 
indeed than 1 grain in 2 lbs. of the soil. 
As this is not a chemical society, we refrain from entering upon the 
details of the method which was pursued, but believe that it would be 
regarded as conclusive, so far as relates to the detection of any con- 
siderable amount of this ingredient ; and with regard to the small pro- 
portion which did exist, it might have been easily derived from the 
attrition of the fragments of phosphorite which were mixed with the 
soil, as we had no means on the spot of sifting it with any accuracy. 
It may therefore be fairly considered that the result of this examina- 
tion confirms the conclusion with regard to the naturally alight tendency 
to decomposition in the mineral, which we had been led to entertain 
from our observation of it on the spot. 
The soil brought home for examination was taken from various parts 
of a corn-field, immediately along the course of the deposit, which we 
were told was in itself by no means productive, but required to be im- 
proved by occasional top-dressings of stable-dung. 
The presence of the phosphate does not, therefore, appear in this 
instance to communicate fertility ; but the compact texture of the stone 
may perhaps render it in its natural state but little adapted for being 
secreted by plants. 
It now only remains that we should state, in conclusion, the 
reasons which have induced us to occupy so much of the time of 
this Society in the description of the deposit alluded to. It has 
been conceived then to deserve a more particular notice. — In the 
first place, because it constitutes, we believe, a solitary instance 
of a rock of any magnitude or extent, as yet known, in which 
phosphate of lime occurs as the prevailing ingredient. 
2ndly. Because the deposit not only contains in itself no traces 
of any organic matter, and possesses a crystalline structure en- 
tirely inconsistent with an organic origin, but also would seem, 
so far as our present knowledge extends, to lie in the midst of 
materials from which the evidences of animal life, if indeed they 
ever existed in them, have been entirely obliterated; for even if 
the fossiliferous slates of Almaden should be determined to be- 
long to the same epoch with those about Logrosan, it must be 
recollected that they are at least fifty miles distant from the latter, 
whilst the existence of phosphate of lime in other instances, 
setting aside a few crystals of apatite occasionally met with in 
mineral veins, seems always referable to the presence either of 
animal exuviae, or of animal excretions in its immediate neigh- 
bourhood. 
3rdly. On account of the exaggerated reports that had been 
