crystalline rock, extremely hard, very cellular, and presenting but few traces of stratification in its interior mass. The weathered surfaces show them however perfectly, as also the concordance of this stratification with that of the overlying and underlying rocks. 11. Secondary bed of dolomite, quite similar in texture and general characters to No. 10, from which it is separated by about 50¤. thick of limestone. It is quite irregular and almost insignificant in thickness, as compared to that of the principal bed.

12. Limestones of a grayish colour, tinged with iron, very loose in their texture, but hard and alternating with beds of marly clay. 13. Brownish clays alternating with thin beds of limestone. 14. Red sandstone of the Escudo mountain.

The beds Nos. 2 and 3 line the south side of the bay of San Vicente, enter the harbour, and form the south-western shore, upon which the principal part of the town has been built. The ease with which they may be eroded would account for the formation of the Ria, or estuary, which constitutes this harbour. On this s.w. shore formerly existed a large boulder of the dolomite, some ten or twelve cubic metres in volume. At the point where the nummulitic limestone crops out on the south-east side of the Ria of San Vicente, about 2km.50 from the principal bridge, beds of dolomite with traces of calamine and galena occur. This dolomite is probably identical with No. 2 in the above table, its reappearance being explained by supposing a synclinal valley extending between this point and the sea-shore. The suc cession may, however, be perfectly regular, in which case we should assume the existence of two beds of dolomite. In either case the occurrence of dolomite here is very interesting, because, firstly, it probably belongs to the tertiary formation, and secondly, from its containing calamine, which would thus be proved to have been deposited during that epoch. In a subsequent part we shall have more to say on this subject. In placing it, however, in the tertiary formation, we do not consider its position as definitely settled, for a closer examination may show that it is really a continuation of the dolomite of Comillas. The existence of beds of Dolomite on the heights between the Rabia and the Ria of San Vicente, near the village of El Tejo, while favouring this latter point of view, does not at all preclude the former. §. 3. Description of Section III., Pl. 2, corresponding to Section FG on Map, and AB, Pl. 5.

The plane of this section traverses the valley of Comillas between Tramalon and the valley of Ruyloba, though closer to the first-named point. All along the trough of this valley, which extends from the mountain stream La Rabia one and a half miles to the west of Comillas, to Tramalon, about two and a half to three

miles to the east, the dolomite presents itself continuously, forming a very distinct anticlinal, and bounded on both sides by limestone beds whose upheaval and subsequent denudation have left it bare (see Plate 4). The dips of the limestone on the north and south sides are variable, being generally highest on the north, along which abundant fossils may be collected, particulariy in the neighbourhood of Venta la Vega, about three quarters of a mile east of Comillas.

In the limestone indicated on the section as immediately overlying the dolomite, are found in great abundance Orbitolina concava, Lam., Rhynchonella depressa, d'Orb., and Terebratula Menardi, Lam. Upon those beds, and towards the sea, rest conformably a thick series of soft green sandstone beds; upon those rest limestone beds, of which a more detailed description will be given further on. Those beds rise about 100m above the level of the sea, forming a hilly chain along the north of the valley. The dolomite exposed here is about 250 to 300m in breadth; it is partially covered over by the highly ochreous earth which constitutes the soil: portions of it, however, stand out here and there, of a deep brown colour and a rugged and weather-beaten appearance, which is eminently characteristic of the dolomite throughout the province. Its stratification is here nearly horizontal, but it dips away to the north and south at the junction with the limestone. This has many deep narrow fissures, some being mere joints, but others are of a sufficient width to have admitted of being subsequently filled up by infiltration from the overlying soil. Traces of calamine and blende are found near the middle, forming a continuation of the Venta metalliferous lode. The dolomite on the south side dips gently to the south, and apparently comes up again in the valley of Pelurgo, a little to the north of that of Udias. The limestone beds which overlie it, and whose stratification near the valley of Comillas varies little from the horizontal, dip, however, to the south, while in that of Pelurgo they dip slightly to the north. In these beds at Ruyloba have been found the fossils.

The beds just described are covered conformably by greenish sandstone (indicated in section III. of Pl. 2 by No. 8, and by the letters s. s. of Pl. 4, the sandstone here not being tinted). Between the valley of Pelurgo and that of Udias lies the range of hills forming the northern side of the latter, as shown in the section, and more fully in Plates 11, 12, and 13. In Pl. 13, a section (a) of the valley indicating the stratigraphical succession of the beds, shows the sandstone and limestone rocks above described overlying the dolomite. The sandstone, however, has been partially eroded, and is only exposed on some of the hills.

Underneath the dolomite, a shelly limestone comes out on the north side of the valley, in which large oysters occur abundantly; the lower bed yields also a fine hydraulic cement, of a peculiarly beautiful cream colour after it has set. The fossil oysters are likewise found in this bed, but not so frequently as in the upper beds. In preparing the cement they are carefully separated, as their presence is injurious to its quality, no doubt because they are almost pure carbonate of lime. A similar bed is found well developed likewise at Novales and Ciguenza, underlying the dolomite. A series of beds of friable sandstone and clay crops out from beneath this limestone; particles of mica are frequent in them, and they seem to have furnished a certain portion of the detritus found in the joints of the underlying limestone. Some of the lower clay beds contain abundant fossils, of which we have not, however, any specimens. In one of the limestone beds immediately in contact with them, corals of a jurassic character have been found covering several metres square on the rise of the old road between the Esmeralda and San Bartolome mines.

A very shelly limestone crops out from under the beds just described. It is the lowest of the series of limestone rocks on the north side of the valley, and is characterised by its frequent fissures, the fineness of its grain, and a gray colour, similar to that of many lithographic stones; it contains abundance of fossils, especially at the San Bartolome mine (situate in the upper part of this bed, although erroneously marked in Pl. 13, as occurring in the upper limestone). A beautiful section of the Nerinaa Goodhallii, Sow., has been found here, as well as a species of Gryphaa, which has all the characters of the Gryphaa arcuata of Lamarck. The frequent occurrence of this lower lias fossil here is singular. The bottom of the valley lies upon beds of red sandstone clay and gypsum, which form the greater part of the elevated ground rising to the west of the valley of Udias, and which, covered with forest trees, is known as the Monte Corona. On the north side of the valley flows a stream which passes under the hills closing in the eastern side, and which, apparently following the strike of some principal fault or joint, as indicated in Plate 13, comes out again in the valley of Novales before falling into the sea. That a fault exists near the bed of the stream is evident from the relative positions of the rocks on the north and south sides of the valley: the limestone which immediately underlies the dolomite on the north side cropping out far above the level of the stream, while on the south side it is found on a level with it, forming indeed its bank. There is here, however, an appaof th alamite with the limestone. whether

it be merely superficial and to be accounted for by chemical metamorphosis or other local action, or peculiar to this part of the formation, there is no evidence to determine. In the lower part of this rock, although about 25 to 30m above the level of the stream, beds of the dull blackish limestone, noticed already as belonging to the northern side, and as furnishing a highly hydraulic cement, may be recognized. The rock here contains hydrocarbonate of zinc, and in it have been found the cave and fossil bones, of which a fuller description will be given when describing the Dolores mine.

The stratification is here nearly horizontal, while on the northern side, where the stratigraphical succession is most marked, the inclination of the beds increases proportionately to their elevation, as is shown by section a, Pl. 13.

The dolomite is here highly fissured, and contains several extensive mines of red calamine, blende, and galena, the principal one being that known as the Angel de Toporias, the works of which pass under the overlying limestone, thus connecting the great mineral deposit found in the dolomite which crops out in the valley of Toporias, with that found in the south side of the valley of Udias. In the hill which bounds this side several faults occur, running generally east and west, and throwing up successively the beds which crop out to the south, over those marked red sandstone and schiste, and which form the north side of the valley of Cabazon de la Sal, while the lower beds of the latter series seem to form the level plain which here intervenes between the river Saya on the north side and the Dobra chain on the south, where the same characteristics present themselves as already described in the details of the preceding section.

Reference has been made at the beginning of the section to the rocks in immediate contact with the Venta mine, where they present peculiarities requiring especial notice. The dolomite at this point is thrown up nearly vertical, as may be seen from the transverse section AB, Pl. 5. The limestone beds on both sides of the valley are also nearly vertical, dipping south. An attentive examination of the relative positions of those beds at different points between the extreme limits of the valley, would lead us to conclude that the bed of dolomite was here so contorted that it formed almost a loop, which, after the denudation of the top, left the parts of the bed forming the anticlinal with apparently the same dip to the south. In Pl. 7 will be found a diagram, in which an attempt has been made to demonstrate by outline sections at different points of the valley, that the dolomite is really inferior in age to the limestone which bounds it to the north and to the south. The outlines 2 and 3

show that this is really the case, while, if we judged by the outline shown by No. 1 alone, we should conclude that the dolomite is posterior to the limestone on the south, but anterior to that on the north, which it seems to overlie conformably. The first two sections in Pl. 6, the planes of which are supposed to pass at two points one quarter of a mile distant from each other, and to the west of the village of Comillas, tend also to prove that the dolomite is anterior. The faults running east and west, and quite recognizable in the neighbouring cliff, which forms the eastern side of Comillas Bay, would have rendered the exact determination of the relative positions of the beds somewhat difficult, were it not for the evidence presented by the cross sections at different other points of the valley. Assuming, then, that the rocks to the north really overlie the dolomite, the age of the former may to a certain extent be determined by the fossils found abundantly in them. Among them may be mentioned Neithea quinquecostatus, Br., Ostrea carinata, Sow., Exogyra haliotoidea, Goldf., Caprina adversa, d'Orb., Terebratula sella, Sow., T. Menardi, Lam., Trigonia dædalia, Parks., and many casts of other species of Ostrea, Pecten, Turrillites, etc.

In order to complete the tabular statement of the succession of rocks as in the former section, it is necessary to describe in some detail the phenomena which are presented by the harbour of Comillas. As has been mentioned above, and as will be seen by the plan of the mines of Comillas (Pl. 5), the valley of Comillas, which runs E. and w., is bounded on both sides by limestone rocks, while its trough is occupied by dolomite. These limestone rocks on the north form, as it were, a great dyke which separates it from the sea, and are cut through by the creek forming the mouth of a small stream, which here runs into the bay after having traversed the narrow valley lying between the bridge called Puente Portillo and Peña Castillo, its general direction being N. and s.

The south-west shore of the bay presents the following succession of rocks:

1. Limestone beds which form a reef of rocks running out towards the N.E., almost completely covered at high water, and full of fossils, but which are so bound together by sparry limestone, into which many of them are converted, that it would be almost impossible to separate them from the corals which are extremely abundant in those rocks.

2. A bed, which is here very thin, though apparently much thicker where it crops out on the headland forming the N.w. side of the harbour, and composed of dark gray nodules mixed up with, or bound together by, an earthy paste of the same colour, apparently very marly.