174 SUBAPENNINE STRATA. [Ci:. XIV. 



the foot of tliese mountains, on the side both of the Adriatic and the 

 Mediterranean, are found a series of tertiary strata, which form, for the 

 most part, a line of low hills occupying the space between the older chain 

 and the sea. Brocchi, as we have seen (p. 110), was the first Italian 

 geologist who described this newer group in detail, giving it the name of 

 the Subapennines ; and he classed all the tertiary strata of Italy, from 

 Piedmont to Calabria, as parts of the same system. Certain mineral 

 characters, he observed, were common to the whole ; for the strata consist 

 generally of light brown or blue marl, covered by yellow calcareous sand 

 and gravel. There are also, he added, some species of fossil shells which 

 are found in these deposits throughout the whole of Italy. 



We have now, however, satisfactory evidence that the Subapennine 

 beds of Brocchi, although chiefly composed of Older Pliocene strata, be- 

 long nevertheless, in part, both to older and newer members of the ter- 

 tiary series. The strata, for example, of the Superga, near Turin, are 

 Miocene ; those of Asti and Parma, Older Pliocene, as is the blue marl of 

 Sienna ; while the shells of the incumbent yellow sand of the same ter- 

 ritory approach more nearly to the recent fauna of the Mediterranean, and 

 may be Newer Pliocene. 



The grayish-brown or blue marl of the Subapennine formation is very 

 aluminous, and usually contains much calcareous matter and scales of 

 mica. TsTear Parma it attains a thickness of 2000 feet, and is charged 

 throughout with marine shells, some of which lived in deep, others in 

 shallow water, while a few belong to freshwater genera, and must have 

 been washed in by rivers. Among these last I have seen the common 

 Limnea 2Mlustris in the blue marl, filled with small marine shells. The 

 wood and leaves, which occasionally formed beds of lignite in the same 

 deposit, may have been carried into the sea by similar causes. The shells, 

 in general, are soft when first taken from the marl, but they become hard 

 when dried. The superficial enamel is often well preserved, and many 

 shells retain their pearly lustre, part of their external color, and even the 

 ligament which unites the valves. No shells are more usually perfect 

 than the microscopic foraminifera, which abound near Sienna, where more 

 than a thousand full-grown individuals may be sometimes poured out of 

 the interior of a single univalve of moderate dimensions. 



The other member of the Subapennine group, the yellow sand and con- 

 glomerate, constitutes, in most places, a border formation near the junction 

 of the tertiary and secondary rocks. In some cases, as near the town of 

 Sienna, we see sand and calcareous gravel resting immediately on the 

 Apennine limestone, without the intervention of any blue marl. Alterna- 

 tions are there seen of beds containing fluviatile shells, with others filled 

 exclusively with marine species ; and I observed oysters attached to many 

 limestone pebbles. The site of Sienna appears to have been a point where 

 a river, flowing from the Apennines, entered the sea when the tertiary 

 strata were formed. 



The sand passes in some districts into a calcareous sandstone, as at San 

 Vignone. Its general superposition to the marl, even in parts of Italy 



