we do not see any reason for considering the London clay as an equivalent of the whole mass of the Paris tertiary limestone; and, as we reject the plastic clay as a distinct formation, arranging it as subordinate to the limestone, we do not see the necessity of a plastic clay in England. No one in England would have thought of separating the plastic clay and the London clay, if that formation had not been proposed and established at Paris; now, however, as that opinion is admitted to be erroneous, it is plain that there is no longer any necessity for searching for it in England. In short, the London basin seems to us to be only a portion of that vast basin of Northern Europe, where the superior deposites predominate, and not at all an equivalent of the Parisian one.

At page 109, on the locality of Haring in the Tyrol, our authors reproach me with having overlooked the marine shells; if, however, they turn to my work on Germany (Geognostiches Gemälde Deutchlands mit rucksicht auf den benachbarten, Landern 1829), they will find, at page 403, that we discuss what genera of marine fossils are to be found there. Häring appears to have been a kind of lagune in a longitudinal valley, which, communicated by some rents with the Bavarian tertiary sea, but the rest of the valley of the Inn was formed by far later fissures, for it does not contain tertiary rocks. On the other hand, it is well known that Häring presents some dubious characters which have induced some observers to place it in the green sand, although still the most plausible arrangement is with the tertiary lignites.

In regard to the Nagelfluh (p. 109), they confess not to be completely acquainted with it; but they lay much stress upon the opinion that it is a tertiary deposite. It cannot be doubted that there are nagelfluh or calcareous conglomerates in the true molasse. Other similar beds occur also in the uppermost tertiary formation, as at Vienna; and even the alluvial soil contains great deposites of nagelfluh, as at Salzburg, and in the Austrian alpine valleys. But there is also another conglomerate, a very thick deposite, which borders some parts of the Alps, especially in Switzerland, which, according to every wellinformed geologist, has very peculiar characters, viz. that it contains not only debris of all the different secondary alpine limestones

and sandstones, but also rounded fragments of primary and secondary crystalline or slaty rocks, which are foreign to the alpine geology. No one but will at once see the high interest of such a composition; and he will find, without surprise, fragments of this rock in the more recent nagelfluhs. Now, these peculiar rocks appear as if dipping under the alpine limestone, while, on the contrary, as along the Lake of Zug and elsewhere, the molasse appears to dip under the first deposite; but no one has been able to confirm the truth of this double position, and nobody ever found in the ancient nagelfluhs any of the shelly beds of the tertiary molasse. For these reasons, we still remain persuaded that it is a secondary deposite, and that its peculiar position in regard to the neighbouring masses of rocks is only an accident, caused by the upheaving, which affected not only the calcareous chain, but also the horizontal tertiary beds. The same peculiar nagelfluh rocks have been found under the greensand of the Voralberg and the Allgau, and again north of Salzburg, and even to the south-east of that town. Lastly, in the middle of the Austrian Alps, the alpine limestone appeared to us to support here and there chalky deposites, at the base of which limestone were seen naglefluh rocks associated with molasse-like rocks. In this last case, as to the north of Salzburg, they contained rolled masses foreign to the mountains composing the Alps. In those places where these foreign boulders were wanting, the chalky deposites were so isolated amongst lofty limestone hills, or surrounded by them as in basin, a situation which sufficiently explains the absence of such boulders or transported rocks, which no force could have brought into such hollows. All these facts brought to our recollection the rocks in the vicinity of the Swiss nagelfluh, and we imagined that we saw there the same connexion of these problematical masses with greensand rocks, as to the south of the Rigi, at the foot of the Pilatus, at Thun, at Saarnen, at the Voirons, &c. We wait now for the dissent or assent of alpine geologists to this statement.

Lastly, We come to our controversy in regard to the age of the Gossau deposite. In their section (Fig. 1.) they have well expressed its unconformable and overlying position upon the alpine limestone, and in a deep and large cavity of that forma

tion. We grant them that similar beds are to be found in some points at the foot of the northern alpine chain. On the other hand, we shall be careful not to compare, as they have done, the position of the Gossau rocks with that of the molasses in the longitudinal valleys of the eastern Alps, and conclude from this false view that rocks of the same age can exist also in the Salzburg alpine valleys, (112). Indeed, most of the valleys of Salzburg are transverse; that of Gossau is of this description; the longitudinal valleys of that country are occupied by lakes, but these do not, any more than the transverse, offer traces of tertiary rocks. These transverse valleys have been formed generally during a period posterior to the tertiary rocks, and the lakes have perhaps occupied more ancient cavities, without directly communicating with the tertiary sea covering the existing flat country. In the same manner, it is acknowledged that the longitudinal valleys of the eastern Alps are far more ancient rents than those which conduct the traveller through the alpine limestone chains. The comparison of our opponents seems so erroneous, and the case of Häring, again brought forward, appears so much of the same description, that we cannot help expressing our astonishment that sets of rocks, so different as those of Häring and Gossau, should be compared together. Lastly, If the valley of Gossau has been filled up by tertiary rocks deposited by an arm of the tertiary sea of the flat country, Why do these same beds not occur throughout the space between Gossau, Gmund, and Saltzburg, in all these great transversal and longitudinal valleys? Hence we cannot see the probability, with our adversaries, that tertiary deposites may have been formed in the valley under examination (112).

On the other hand, they remark, that there is a great break between the chalk and the calcaire grossiere or tertiary inferior limestone (182), and that a deposite somewhere fills up the interval, and connects the tertiary soil with the chalk. The hill of St Peter, at Maestricht, owing to its containing a mixture of secondary and tertiary fossils, is proposed as an example of this kind. First, after reproaching me with comparisons taken in distant countries, it seems that my critics expose themselves still more than I to this objection, for Maestricht is very far from Gossau, and that limestone bears but little resemblance to that of Gossau,

Besides, the small number of

in its position, nature, and fossils. similar petrifactions is of no consequence, because this accident can be explained by placing both deposites in the chalk, as well as by classifying both in the tertiary soil. But most conchologists and geologists still consider the bacculite limestone of Maestricht and of Valognes, which resembles that of the Danish Isles, as a part of the chalk formation.

After having considered the deposite of Maestricht, we return to the reasoning, apparently fair, that the tertiary soil appears always to be separated from the chalk by a break. Our adversaries forget that there are a good many similar cases in geology. Thus, in certain basins, the old alluvium (diluvium of some English geologists) occupies a higher level than the modern alluvium; the two deposites are not intermixed either by transition or alternation; because, probably, sudden ruptures, various catastrophes, have occasioned a sudden sinking of the level of the water during the alluvial period. Besides, how many formations, deposites, and even beds, are not placed in unconformable and overlying stratification, the one upon the other, in consequence of accidents occasioned by upheaving, slipping down, and total overturning, which have affected the inferior masses, before the deposite of the superior ones? The case of the chalk seems to us a very simple one, for we do not see the necessity of its being connected, at least in Europe, with the tertiary soil; at the same time, we do not deny that such may be the case in other parts of the world: allowing such a possibility, we do not see the necessity for a new and unknown formation to effect such an insensible transition. We agree with many eminent geologists in thinking that, in Europe, the termination of the chalk period was characterized by tremendous catastrophes; whole chains of mountains have been heaved up, immense lines of volcanic eruptions first made their appearance, and in consequence most dreadful and great ruptures took place, and whole continents were thrown up. In this way, the sea would leave dry a great part of the countries it formerly covered, and the deposites formed under its surface, or along the shores, would naturally occur in unconformable and overlying stratification, sometimes in gulfs surrounded by steep chalk-cliffs, sometimes in primary or secondary creeks. The immense changes that took

place at that period are fully adequate to explain why whole classes of animals, as belemnites, &c. and even of vegetables, disappeared from Europe, and that other animals and plants took their origin, or sprang into existence from this new state of things.

In pursuing our examination of the reasoning of our adversaries, we were startled with the following remark,-" that if the Eastern Alps have been elevated at so recent a period, there must be on their flanks a continuous succession of deposites between the new secondary, and the older tertiary periods,” (112). We really do not see the force or meaning of this observation, for we cannot see what an upheaving, may it even be alluvial, has to do with the existence of certain deposites, for very few formations, and especially the more recent ones, are generally distributed over the whole surface of the globe. The deposites wished for may, or may not, have existed along the Alps; but the fact is, that no one, excepting our authors, have found a trace of them.

We agree with our authors" that the age of the Gossau beds must be determined by their relations, structures, and fossils, and that there is nothing in their relations and structure which proves them to be older than the chalk (including the greensand). Besides, we confess that the appearance of many, and even of the greater number of the Gossau fossils, is tertiary, from their state of preservation, the great preponderance of univalves over bivalves, and the incredible abundance of shells of certain genera, seldom found except in the newest formations,” (p. 112). But, on the other hand, we find ourselves brought back to the secondary class by the gryphites, catillus, inoceramus, neritina, trigonia, plicatula, the pecten quinquecostatus, &c. If, contrary to acknowledged geological principles, we neglect the difficulty occasioned by the presence of secondary chalk fossils, and attend only to the tertiary shells, shall we be right or wrong in maintaining that the deposite is newer than chalk? We do not believe that this mode of proceeding is allowed; and we are gratified to find our opinion agree with that of men well fitted for judging of such difficulties. First, if Mr Alexander Brongniart classifies, as do our opponents, the greensand of the Kressenberg in the tertiary class, it is because he has been shewn only the tertiary genera ;