520 A. L. ADAMS ON VERTEBRATA OF THE 
character of the rock and its components. The most interesting 
are four well-marked seams of nodules, which differ considerably. 
Many of these lumps contain casts of Mollusca, and display appear- 
ances of having been rolled. They may be irregular in shape and 
consistence, or polished and rounded. The following is the result 
of very many careful examinations of cliff- and horizontal sections of 
this formation made by me during five years’ work on the Maltese 
deposits. 
The uppermost portion of the bed is composed of a pale grey 
freestone, soft and easily worked. Traversing this bed is a band of 
nodules, for the most part rounded and loosely arranged: it often 
thins out to a mere indication of a bed; indeed it would seem to 
be sometimes wanting. This, the First Nodule seam, is generally 
characterized by the abundance of casts of what have been supposed 
to be a Pteropod allied to Hyalea, and a Vaginella undistinguish- 
able from V. depressa. 
About eight feet below the last nodule-seam, in a fawn-coloured 
sandstone, is the Second Nodule seam, which is readily distin- 
guished, not only from its position but from the small round nodules 
and their loose arrangement. They are usually of a brown colour ; 
and when broken present no apparent characters distinct from those 
of the parent rock. The thickness of the band is often from three to 
four feet. It abounds with organic remains, and has produced 
nearly all the Vertebrata and the majority of the Invertebrata of the 
Calcareous Sandstone. It is a famous horizon from which the teeth 
of Squalide are obtained. 
About the middle of the bed a few scattered nodules of a light 
green colour extend in broken lines, but rarely agglomerated ; and 
they are not unfrequently absent. 
About thirty feet below the second seam is the Third, distin- 
guishable by the irregular shape of its nodules, which are of a dark 
brown colour, firmly cemented together, and apparently of the same 
mineral structure as the parent rock. They repose on a surface 
broken up by pot-holes and crevices, in which many of the nodules 
are contained. This stratum is highly fossiliferous; but, from the 
firmness and hardness of the matrix, organic remains are extracted 
with difficulty. It varies in thickness from | to 4 feet, and may be 
seen to the greatest advantage on the shore-line westward of the 
lighthouse of Gozo. 
From twenty-four to forty feet below the last is the Fourth Seam 
in a pale-coloured sandstone. It is made up of lght-brown 
nodules of irregular shape and of variable thickness. It marks the 
point of transition between the Calcareous Sandstone and Lower 
Limestone beds. Sometimes a seam of rounded nodules of lime- 
stone traverses the rock in place of these calcareous nodules; the 
former differ in their waterworn aspect and the great firmness of 
their matrix, which is composed of fragments of shells of various 
forms found in both formations. Moreover the fourth nodule seam 
may be replaced by lines of broken shells. 
As to the mineral composition of the nodules generally, I repeat 
