double occipital condyles only met with in mammals, and the convoluted tympanic bones which are characteristic of cetaceans.

Near the junction of No. 2 and the incumbent limestone, No. 3, next to be mentioned, are strata characterized by the following shells: Spondylus dumosus (Plagiostoma dumosum, Morton), Pecten Poulsoni, Pecten perplanus, and Ostrea cretacea.

No. 3 (fig. 273) is a white limestone, for the most part made up of the Orbitoides of D'Orbigny before mentioned (p. 309), formerly supposed to be a nummulite, and called N. Mantelli, mixed with a few lunulites, some small corals, and shells.* The origin, therefore, of this cream-colored soft stone, like that of our white chalk, which it much resembles, is, I believe, due to the decomposition of these foraminifera. The surface of the country where it prevails is sometimes, marked by the absence of wood, like our chalk downs, or is covered exclusively by the Juniperus Virginiana, as certain chalk districts in England by the yew tree and juniper.

Some of the shells of this limestone are common to the Claiborne beds, but many of them are peculiar.

It will be seen in the section (fig. 273, p. 310) that the strata Nos. 1, 2, 3 are, for the most part, overlaid by a dense formation of sand or clay without fossils. In some points of the bluff or cliff of the Alabama River, at Claiborne, the beds Nos. 1, 2 are exposed nearly from top to bottom, whereas at other points the newer formation, No. 4, occupies the face of nearly the whole cliff. The age of this overlying mass has not yet been determined, as it has hitherto proved destitute of organic remains.

The burr-stone strata of the Southern States contain so many fossils agreeing with those of Claiborne, that it doubtless belongs to the same part of the Eocene group, though I was not fortunate enough to see the relations of the two deposits in a continuous sec

*Lyell, Quart. Journ. Geol. Soc., 1847, vol. iv. p. 15.

tion. Mr. Tuomey considers it as the lower portion of the series. It may, perhaps, be a form of the Claiborne beds in places where lime was wanting, and where silex, derived from the decomposition of felspar, predominated. It consists chiefly of slaty clays, quartzose sands, and loam, of a brick-red color, with layers of cellular chert or burr-stone, used in some places for mill-stones.

Lapse of time between the Cretaceous and Eocene periods-Whether certain formations in Belgium and France are of intermediate age-Pisolitic limestone-Divisions of the Cretaceous series in North-Western Europe-Maestricht beds-Chalk of Faxoe-White chalk-Its geographical extent and origin-Formed in an open and deep sea-How far derived from shells and corals-A similar rock now in progress in the depths of the Atlantic made up of Globigerina-Origin of Flint in Chalk-Siliceous Diatomacea of the Atlantic-By what intermittent action the alternate layers of white chalk and flint may have been caused-Potstones of Horstead-Isolated pebbles of quartz and foreign rocks in chalkFossils of the Upper Cretaceous rocks-Echinoderms, Mollusca, Bryozoa, Sponges Upper Greensand and Gault-Blackdown beds-Flora of the Upper Cretaceous period-Fossil plants of Aix-la-Chapelle-Large proportion of Dicotyledonous Angiosperms-Their coexistence with large extinct genera of reptiles -Chalk of South of Europe-Hippurite limestone-Cretaceous rocks of the United States.

HAVING treated in the preceding chapters of the tertiary strata, we have next to speak of the uppermost of the secondary groups, commonly called the chalk or the cretaceous strata, from creta, the Latin name for that remarkable white earthy limestone, which constitutes an upper member of the group in those parts of Europe where it was first studied. The marked discordance in the fossils of the tertiary, as compared with the cretaceous formations, has long induced many geologists to suspect that an indefinite series of ages elapsed between the respective periods of their origin. Measured, indeed, by such a standard, that is to say, by the amount of change in the Fauna and Flora of the earth effected in the interval, the time between the Cretaceous and Eocene may have been as great as that between the Eocene and Recent periods, to the history of which the last seven chapters have been devoted. Several fragmentary deposits have been met with here and there, in the course of the last half century, of an age intermediate between the white chalk and the plastic clays and sands of the Paris and London districts, monuments which have the same kind of interest to a geologist which certain mediaval records excite when we study the history of nations. For both of them

throw light on ages of darkness, preceded and followed by others of which the annals are comparatively well known to us. But these newly-discovered records do not fill up the wide gap, some of them being closely allied to the Eocene, and others to the Cretaceous type, while none appear as yet to possess so distinct and characteristic a fauna as may entitle them to hold an independent place in the great chronological series.

Among the formations alluded to, the Thanet Sands of Prestwich have been sufficiently described in the last chapter, and classed as Lower Eocene. To the same tertiary series belong the Belgian formations, called by Professor Dumont, Landenian and Heersian, although the latter may be of higher antiquity than the Thanet Sands. On the other hand, the Maestricht and Faxoe limestones are very closely connected with the chalk, to which also the Pisolitic limestone of France has been referred by high authorities.

The Lower Landenian beds of Belgium consist of marls and sands, often containing much green earth, called glauconite. They may be seen at Tournay, and at Angres, near Mons, and at Orp-le-Grand, Lincent, and Landen in the ancient province of Hesbaye, in Belgium, where they supply a durable building-stone, yet one so light as to be easily transported. Some few shells of the genus Pholadomya, Scalaria, and others, agree specifically with fossils of the Thanet Sands; but most of them, such as Astarte inæquilatera, Nyst, are peculiar. In the building-stone of Orp-le-Grand, I found a Cardiaster, a genus which, according to Professor E. Forbes, was previously unknown in rocks newer than the cretaceous.

Still older than the Lower Landenian is the marl, or calcareous glauconite, of the village of Heers, near Waremme, in Belgium; also seen at Marlinne in the same district, where I have examined it. It has been sometimes classed with the cretaceous series, although as yet it has yielded no forms of a decidedly cretaceous aspect, such as Ammonite, Baculite, Belemnite, Hippurite, &c. The species of shells are for the most part new; but it contains, according to M. Hébert, Pholadomya cuneata, an Eocene fossil, and he assigns it with confidence to the tertiary series.

Pisolitic limestone of France.-Geologists have been still more at variance respecting the chronological relations of this rock, which is met with in the neighborhood of Paris, and at places north, south, east, and west of that metropolis, as between Vertus and Laversines, Meudon, and Montereau. It is usually in the form of a coarse yellowish or whitish limestone, and the total thickness of the series of beds already known is about 100 feet. Its geographical range, according to M. Hébert, is not less than 45 leagues from east to west, and 35 from north to south. Within these limits it occurs in small patches only, resting unconformably on the white chalk. It was originally regarded as cretaceous by M. E. de Beaumont, on the ground of its having undergone, like the white chalk, extensive denu

tion. Mr. Tuomey considers it as the lower portion of the series. It may, perhaps, be a form of the Claiborne beds in places where lime was wanting, and where silex, derived from the decomposition of felspar, predominated. It consists chiefly of slaty clays, quartzose sands, and loam, of a brick-red color, with layers of cellular chert or burr-stone, used in some places for mill-stones.

Lapse of time between the Cretaceous and Eocene periods-Whether certain formations in Belgium and France are of intermediate age-Pisolitic limestone-Divisions of the Cretaceous series in North-Western Europe-Maestricht beds-Chalk of Faxoe-White chalk-Its geographical extent and origin-Formed in an open and deep sea-How far derived from shells and corals-A similar rock now in progress in the depths of the Atlantic made up of Globigerinæ—Origin of Flint in Chalk-Siliceous Diatomaceæ of the Atlantic-By what intermittent action the alternate layers of white chalk and flint may have been caused-Potstones of Horstead-Isolated pebbles of quartz and foreign rocks in chalkFossils of the Upper Cretaceous rocks-Echinoderms, Mollusca, Bryozoa, Sponges-Upper Greensand and Gault-Blackdown beds-Flora of the Upper Cretaceous period-Fossil plants of Aix-la-Chapelle-Large proportion of Dicotyledonous Angiosperms-Their coexistence with large extinct genera of reptiles -Chalk of South of Europe-Hippurite limestone-Cretaceous rocks of the United States.

HAVING treated in the preceding chapters of the tertiary strata, we have next to speak of the uppermost of the secondary groups, commonly called the chalk or the cretaceous strata, from creta, the Latin name for that remarkable white earthy limestone, which constitutes an upper member of the group in those parts of Europe where it was first studied. The marked discordance in the fossils of the tertiary, as compared with the cretaceous formations, has long induced many geologists to suspect that an indefinite series of ages elapsed between the respective periods of their origin. Measured, indeed, by such a standard, that is to say, by the amount of change in the Fauna and Flora of the earth effected in the interval, the time between the Cretaceous and Eocene may have been as great as that between the Eocene and Recent periods, to the history of which the last seven chapters have been devoted. Several fragmentary deposits have been met with here and there, in the course of the last half century, of an age intermediate between the white chalk and the plastic clays and sands of the Paris and London districts, monuments which have the same kind of interest to a geologist which certain mediæval records excite when we study the history of nations. For both of them

throw light on ages of darkness, preceded and followed by others of which the annals are comparatively well known to us. But these newly-discovered records do not fill up the wide gap, some of them being closely allied to the Eocene, and others to the Cretaceous type, while none appear as yet to possess so distinct and characteristic a fauna as may entitle them to hold an independent place in the great chronological series.

Among the formations alluded to, the Thanet Sands of Prestwich have been sufficiently described in the last chapter, and classed as Lower Eocene. To the same tertiary series belong the Belgian formations, called by Professor Dumont, Landenian and Heersian, although the latter may be of higher antiquity than the Thanet Sands. On the other hand, the Maestricht and Faxoe limestones are very closely connected with the chalk, to which also the Pisolitic limestone of France has been referred by high authorities.

The Lower Landenian beds of Belgium consist of marls and sands, often containing much green earth, called glauconite. They may be seen at Tournay, and at Angres, near Mons, and at Orp-le-Grand, Lincent, and Landen in the ancient province of Hesbaye, in Belgium, where they supply a durable building-stone, yet one so light as to be easily transported. Some few shells of the genus Pholadomya, Scalaria, and others, agree specifically with fossils of the Thanet Sands; but most of them, such as Astarte inæquilatera, Nyst, are peculiar. In the building-stone of Orp-le-Grand, I found a Cardiaster, a genus which, according to Professor E. Forbes, was previously unknown in rocks newer than the cretaceous.

Still older than the Lower Landenian is the marl, or calcareous glauconite, of the village of Heers, near Waremme, in Belgium; also seen at Marlinne in the same district, where I have examined it. It has been sometimes classed with the cretaceous series, although as yet it has yielded no forms of a decidedly cretaceous aspect, such as Ammonite, Baculite, Belemnite, Hippurite, &c. The species of shells are for the most part new; but it contains, according to M. Hébert, Pholadomya cuneata, an Eocene fossil, and he assigns it with confidence to the tertiary series.

Pisolitic limestone of France.-Geologists have been still more at variance respecting the chronological relations of this rock, which is met with in the neighborhood of Paris, and at places north, south, east, and west of that metropolis, as between Vertus and Laversines, Meudon, and Montereau. It is usually in the form of a coarse yellowish or whitish limestone, and the total thickness of the series of beds already known is about 100 feet. Its geographical range, according to M. Hébert, is not less than 45 leagues from east to west, and 35 from north to south. Within these limits it occurs in small patches only, resting unconformably on the white chalk. It was originally regarded as cretaceous by M. E. de Beaumont, on the ground of its having undergone, like the white chalk, extensive denu