510 
gained by tlie accidental discovery of a few lower jaws at the 
bottom of a shaft, G2 feet in depth.* These minute fossils, ten 
only in number, have been referred to three genera ; Amphi- 
therium, Phascolotherium, and Stereognathus ; and they are all 
the remains we at present possess of the mammalian life of Europe, 
during the long period represented by the lower Oolitic deposits. 
From the middle Oolite no such remains have been discovered, nor 
have there been any from the Kimmeridge clay, nor the Portland 
beds, which have together a maximum thickness of 700 feet. 
In the Purbeck beds, however, from an area 500 square yards in 
extent, and from a bed a few inches in thickness, have been taken 
what, compared with those I have mentioned before, seems a large 
collection. Although eight or nine genera, and fourteen species of 
quadrupeds have been described from these beds, the complete 
skeleton of none of them is known. The specimens are princi- 
pally lower jaws, one, however, being a portion of a cranium. 
Sir Charles Lyell makes the following pertinent remarks on 
the discovery of these fossils : — t “But the most instructive lesson 
read to us by the Purbeck strata consists in this : they are all, 
with the exception of a few intercalated brackish and marine 
layers, of fresh -water origin; they are 1G0 feet in thickness, have 
been well searched by skilful collectors, and by the late Edward 
Forbes in particular, who studied them for months consecutively. 
They have been numbered, and the contents of each stratum 
recorded separately, by the officers of the Geological Survey of 
Great Britain. They have been divided into three distinct groups 
by Forbes, each characterized by the same genera of pulmoniferous 
mollusca and cyprides, these genera being represented in each 
group by different species ; they have yielded insects of many 
orders, and the fruits of several plants; and, lastly, they contain 
‘ dirt-beds,’ or old terrestrial surfaces, and vegetable soils, at different 
levels, in some of which erect stumps and trunks of cycads and 
* A. fibula, and a humerus of a small mammal have recently been 
discovered in a slab of Stonesfield slate, which lias been lying for many years 
in the British Museum. 
t Lyell’s Elements of Geology , p. 386. 
