| OCR Text |
Show 162 OLDER PLIOCENE PEit.IOD· [Ch, XII. • .l' hastily a contemporaneous h 1 . t not to lOler too . tot e geo ogts ' . 1 position. The depostt of f 'd t'ty of mmera com origin rom 1 en 1 1 at the bottom of a deep V 1 d' Arno occurs near y the Upper a . nded by precipitous rocks of 11 y which 1s surrou . narrow va e ' d b 1 (the maciano of the Itahans and d dstone an s a e 0 secon ary san ) Hills of yellow sand, of con-greywacke of the Germans · und the margin of the small 1 h' k s appear aro siderab e t lC nes ' h tral parts where there has been b . bile towards t e cen ' 1 asm, w ' . d here the Arno flows, b ue clay · d ble denudatiOn, an w cons1 era . h 11 sand. The shells are of fresh- . en under1ymg t e ye ow . 1 f h IS se . . 1 11 speak more particular yo t em t r origm but we sla . . 1 wa e . ' h bable age of this formation m t 1e when we discuss t e pro 11 h d , W desire at present, to ca t e rea er s sixteenth chapter. e ' . . 1 d b . ttention to the 1la' ct, th a t we have here, m an ISOf a teb asm., as uch a formati.o n as wou ld result from the waste o t e co1n. t lh· uous secondary rock s 0 f the Apennines, fragments of wd u c gro cks are foun d m. t 1J e san d and conglomerate. We shoul e.x - ect that t. f the f resh wa t er beds were. re.m oved, . and the bamer Po f the lake-b as.m c1 o se d up again , similar sediment wou.l d be agam. depos1. te d , .1l' 0r the aqueous agents w.o uld ope.r ate m.. t he same manner, at wh a t ever period they m1gh. t. be bm actmtyI . Now the on 1y d I.. utre r ence ' in mineral compositiOn, . etween t. 1e lacus' trm. e d eposl' t ab o ve alluded to, . and. the orbd mary mfa rm1e f h S bapennine beds, conststs m the a sence o ca - strata o t e u fl · · t th 1 ke careous matter f rom th e clay ' the torrents owmg m o e a . assed over no limestone rocks. . . ha;.~ f;thological character of the Subapennine beds var;e< :~ d'ffi rent parts of the peninsula both in colour and degree o so~ d~ t e The presence, also, or absence of lignite and gypsum, an 1 y. . . non-association of volcanic rocks, are causes the associatiOn or · · f the sand and 1 d' cy The superpositiOn o of grleat loc; t~s~~:P:arl. on the other hand, is a general point cong omera e ' · t tb rule as at f ment although there are exceptiOns o e ' o a<Tree ' f b' ·ancrement San oQ uirico before men ti.O ne d . The cause o t IS art o ere may be, as we before hinted, that th~ arenaceo~~ gro::s '~len fi rst 1t'o rme d on the coast where nvers enteie ' a Ch. XII.] ORGANIC REMAINS OF SUBAPENNINES, 163 these pushed their deltas farther out, they threw down the sand upon part of the bed of the sea already occupied by finer and more transportable mud. Organic Remains.-! have been informed, by experienced collectors of the Subapennine fossils, that they invariably procure the greatest number in those winters when the rains are most abundant, an annual crop, as it were, being washed out of the soil to replace those which the action of moisture, frost, and the rays of the sun, soon reduce to dust upon the surface. 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, and even part of their external colour, and the ligament which unites the valves. No shells are more usua1Iy perfect than the microscopic, which abound near Sienna, where more than a thousand full-grown individuals are sometimes poured out of the interior of a single univalve of moderate dimensions. In some large tracts of yellow sand it is impossible to detect a single fossil, while in other places they occur in profusion. The Subapennine testacea are referrible to species and fami· lies of which the habits are extremely diversified, some Jiving in deep, others in shallow water, some in rivers or at their mouths. I have seen a specimen of a fresh-wate·r univalve (Limnea pa1ustris), taken from the blue marl near Parma, full of small marine shells. It may have been floated down by the same causes which carried wood and leaves into the ancient sea. Blocks of Apennine limestone are found in this formation drilled by lithodomous shells. 'rhe remains not only of testacea and corals, but of fishes and crabs, are met with, as also those of cetacea, and even of terrestrial quadrupeds. A considerable list of mammiferous species has been given by Brocchi and some other writers; and, although several mistakes have been made, and the bones of cetacea have sometimes been confounded with those of land animals, it is still indubitable that the latter were carried down into the sea when the Subapennine sand and marl were accumulated. The same M2 |
