Fissures In Limestone Research Articles

Data-model comparisons of isotopic and hydrological variabilities of the karstic vadose zone above Villars Cave, SW-France based on 20 years' monitoring record

Because of the great heterogeneity of the limestone fissures, conduits, and reservoirs in karst areas, the understanding of the infiltration in caves and karst terrains is complicated. For example, the time delays observed between rainfall and the various flows into caves, such as shaft flow and seepage flow, exhibit significant variability. To better understand the infiltration above a typical shallow cave, Villars Cave, South-west France, we used both a very long monitoring (>20 years) isotopic data set of rainfall and dripping rates at two different cave gallery levels (14 m and 36 m below the surface, respectively) and a conceptual model (KarstFor) that mix water flows and isotopes. In order to determine the most appropriate reservoir and flow settings, we used one time-lapse electrical resistivity tomography (ERT) image made above the cave, which were incorporated into the KarstFor model. The modeled variations in storage water and infiltration flows are in a good agreement with the observed dripping discharge rates, indicating seasonal variability and various time delays between water excess ((Rainfall-Evapotranspiration) > 0) and drip rates in the different cave levels. The fact that the model strikingly simulates the small, but constant, isotopic difference of drip water δ18O (δ18Od) values between the upper and the lower galleries of Villars Cave, not only reinforces reliability in the model itself but also reveals the impact of multiple infiltration routes and karst reservoir dynamics on the δ18Od. On an inter-annual scale, the observed δ18Od values follow the variations of the water excess and of the cave temperature, which, in the period analyzed, show a marked trend, possibly induced by the climate variability patterns above the cave. Overall, these results are not only important to better understand the infiltration in karstic zones, but also to better interpret speleothem isotopic records widely used in paleo-climate studies.

Investigation and characterization of karst landform with GPR: a case study in Shandong, China

A substation is an important infrastructure for city operation and people’s life. The proposed site, 37 km northeast of Zaozhuang, Shandong province, is located on top of Cambrian limestone, most of which is directly exposed or covered by thinner Quaternary silty clay. The Karst processes on the surface contribute to the dissolution of gullies and limestone fissures in the surface topography. Directly the evidence shows that the study area is karst cave or the possibility of larger crack, the potential risk impact on subsequent substation the safety of the pile foundation installation construction. Thus led to the ground penetrating radar (GPR) investigation on the bedrock of karst development. The aim of this study was to characterize the development of karst caves in the shallow surface and delineate their locations. The 80 MHz shielding antenna was used to study and characterization of the karst features. The results of GPR method show that the application of a low-frequency antenna can satisfy a certain detection depth and well characterize the development of underground karst, which also proves that GPR method is very practical in the detection of karst landform and can be applied to identify similar geomorphic features.

Deterioration Processes on Prehistoric Rock Art Induced by Mining Activity (Arenaza Cave, N Spain)

Arenaza Cave is located in Vizcaya (N Spain) and contains important Palaeolithic rock art representations. This cave belongs to an active karstic system developed on Lower Cretaceous limestones, mainly consisting of micrites and biomicrites with abundant pyrite moulds. The paintings are made directly on the host rock or on thin stalagmitic calcite crusts. Cretaceous limestones in this area contain important iron ore deposits, which have been mined by subsurface and surface-mining methods since the beginning of the 20th century. Mining activities have induced significant changes in the karstic drainage pattern and in the endo and exokarstic morphologies of the Arenaza karstic system, directly affecting the state of conservation of the prehistoric paintings. Thus, in addition to natural process of deterioration, the enlargement of the limestone fissure system as a result of blasting-induced vibrations seems to be the responsible for changes in the rates of water-rock interactions and of the formation of botryoidal gypsum concretions on the rock surface. The final result is the activation and acceleration of detachment processes and the increase of irreversible deterioration processes in the cave.

Soil structure and nutrient contents in underground fissures in a rock-mantled slope in the karst rocky desertification area

Near-surface karst fissures are filled with soils. These soils are often derived from the erosion and transport of surface soil but have different properties than the surface soil in karst rocky desertification regions. This study was undertaken to determine the soil structure and nutrient contents in underground fissures with different grades of rocky desertification (no, potential, mild, moderate and severe). Based on field surveys, near-surface karst fissures were selected in a typical karst plateau area. Soil particle compositions, particularly nutrient characteristics, were determined through field sampling and laboratory experiments. The results indicated that the higher the rock desertification grade was, the higher the soil sand (0.02–2 mm) content and the lower the clay (< 0.002 mm) content. The soil in both limestone and dolomite fissures was basically neutral to weakly alkaline. The surface soil in dolomite fissures presented a higher soil organic matter content than that in limestone fissures, but the opposite was true for the subsurface soil. From the surface to the lower layer, the total nitrogen content generally decreased, and the total phosphorus content generally decreased in dolomite fissures but exhibited a more complex pattern in limestone fissures. The total phosphorus content of the surface soil was higher than that of the subsurface soil, but the total potassium content was lower. There was no significant difference among different soil layers. Near-surface fissures are a good place to promote vegetation restoration projects, because they provide good soil structure and nutritional conditions for plant growth.

Use of nutrient medium technique for vegetation restoration in Karst region of Southwest China

Karst rocky desertification (KRD) is a global environmental degradation problem caused by human activities and vegetation deterioration. Vegetation restoration in KRD is very difficult due to severe water loss, soil erosion and extensive bare bedrock. For achieving vegetation restoration on bare bedrock areas of KRD, the nutrient medium technique was developed, which is based on the special hydro-geological conditions that is seasonal rainfall is abundant in Karst region of Southwest China and limestone fissures are extremely developed and rich in fissure water. The objective of this research is to investigate the feasibility of using nutrient medium technique to achieve vegetation restoration in KRD region. Through the indoor and field experiments, some properties of the nutrient medium mixture were tested, including water retention, water absorption and nutrient retention. The results showed that the moisture content on the 75th day and water absorption rate of No.2 mixture was 19.9% and 1.67 mm/d, respectively, which could be used as optimum mix ratio for producing nutrient medium. The field results showed that the nutrient medium technique could effectively guarantee the survival of sapling at early age and sustainable growth at later age in the field, and the nutrient medium had less nutrient loss. This novel approach can retain and absorb moisture, and saplings do not need artificially supply water and fertiliser in the dry season, and the use of nutrient medium technique to achieve vegetation restoration in KRD region seems to be a feasible option.

Дослідження слідів вилуговування в ізвестнякпах континентального схилу Криму

The paper is about the leaching process. Processes are common in almost all calcareous rocks of Crimea. They meet in the F irst ridge of the Crimean Mountains in the Neogene and Paleogene rocks, as well as in the Jurassic limestone of the Main ridge of Crimean mountains. A large number of geological and tourist sites associated with chemical weathering process, named in honor of the Slovenian Karst. Among the typical karst plateau consists of a large number of fascinating caves to a depth of 500 m. As well as smaller form. They are distributed in almost all types of limestones of the Crimean peninsula. However, not all forms of leaching have classic karst origin. Particularly interesting findings with clear signs of leaching on the seabed, raised in several expeditions OMGOR NAS of Ukraine when working on the Crimean continental slope, at the latitude of Cape Foros. About weathering Mesozoic rocks of the seabed of the Black Sea is known very little. Only in the Yu.G. Balandin and V.I. Miller describes the properties of the weathering crust Jurassic shale strata shelf southern coast. On the continental slope Crimea leached rocks were first raised in the 80s geological expeditions Department of Marine Geology and Sedimentary Ore (OMGOR). In the works of Ye.F. Shnyukov, Yu.Yu. Orovetskiy dense limestone with spongy voids leaching dated lower chalk have been described. In subsequent flights OMGOR NAS of Ukraine repeatedly met limestones, mudstones, travertine with different forms of weathering, including emissions of solid mud volcanoes. Forms of weathering in the Crimean Mountains, besides the classic speleogeneticaly genesis, can be formed at the contact of limestone strata of the Upper Jurassic to the lower chalk. These boundaries are observed traces of erosion and karst phenomena. This indicates the presence of a significant erosion between the Jurassic and Cretaceous. The Upper Jurassic limestone rocks spread from the border plateau Karaby-Yayla to Cape Fiolent. Rocks presented thin-layered clean and brecciated limestones. Studies have shown that the geological history of the Crimean Mountains and the deep-sea basin of the Black Sea have the same course of the processes. The test is a limestone facies Shallow Upper Jurassic age, and have been leaching at rewashing on the border of the Jurassic and Cretaceous. The limestone fissures silicification was formed as a result of the activity of living organisms. As a result, silica katagenesis finally formed in the quartz in the Upper Cretaceous. Column was down to great depths, and is a component of the continental slope in the present form. Most likely, fragments of limestone have been omitted hypsometrically lower levels on the occurrence of Cretaceous strata, as a result of neotectonic and landslides.

Effects of land use, land cover and rainfall regimes on the surface runoff and soil loss on karst slopes in southwest China

Abstract Surface runoff and soil loss from 2007 to 2010 related to land use and rainfall regimes in karst hill slopes in Guizhou Province, southwest China, were analyzed. Using the hierarchical clustering method, sixty-one rainfall events under the subtropical monsoon climate condition were classified into 5 types of rainfall regimes according to the depth, maximum 30-min intensity, and duration of rainfall. In our study, we first demonstrated that the amounts of surface runoff and soil loss on the karst hill slopes were very small compared to the non-karst areas, because the dual hydrological structure in the karst region, including ground and underground drainage systems, could influence the processes of rainfall recharge and runoff generation. Most rainfall water was transported underground through limestone fissures and fractures, while little was in the form of surface runoff. Second, the runoff and soil loss were affected by land use management and vegetation cover. Soil loss was intensified in a descending order to five types of land uses: pastureland > burned area > cropland > combination vegetation land > young forestland. Third, the runoff and soil loss exhibited remarkable variances among different rainfall regimes. Large runoff and soil loss were mainly created by heavy rainfall storms with a rainfall depth of more than 40 mm and a maximum 30-min rainfall intensity of over 30 mm h− 1. In addition, rainfall storms with large antecedent precipitations could also produce large runoff and soil loss. These observations indicated that limestone fissures and fractures play important roles in surface runoff generation on karst limestone slopes due to their large storage capacity and high infiltration rate. Lastly, the soil erosion risk in the karst pure limestone slope is quite high and should be paid particular attention, especially in regards to over-grazing because the soil loss created by a single heavy rainstorm in pastureland was 5 times the annual soil loss tolerance.

An Early Permian varanodontine varanopid (Synapsida: Eupelycosauria) from the Richards Spur locality, Oklahoma

ABSTRACT Description of the first varanodontine varanopid material from the highly fossiliferous limestone fissure fill deposits at Richards Spur (Dolese Brothers Limestone Quarry), Oklahoma, is based on elements of at least three individuals recovered from two separate blocks of sedimentary rock. One block, which yielded associated cranial and postcranial bones from both adult and juvenile individuals, includes two well-preserved parabasisphenoid complexes, vertebrae, forelimb, pelvic girdle, and hind limb bones. An isolated maxilla fragment from another block preserves the diagnostic dorsal process characteristic of varanodontines. Preserved cranial and postcranial material is virtually identical to the varanodontine Varanops brevirostris. Taxonomic assessment of this new material in the context of the most comprehensive phylogenetic analysis of Varanopidae to date indicates the Richards Spur varanodontine is referable to Varanops brevirostris based on distinctive characters of the maxilla and the parabasisphenoid. The large size of Varanops suggests it was one of the top predators of the Richards Spur ecosystem. The Richards Spur locality records the only known co-occurrence of a mycterosaurine and a varanodontine varanopid at a single locality, and varanopids are the most common synapsids in the assemblage. As generally rare components of the more typically preserved lowland environments, the relative abundance and diversity of varanopids at Richards Spur suggests that they may have been more common components of the upland ecosystems in the Early Permian.

Influence of aperture variability on dissolutional growth of fissures in Karst Formations

The influence of aperture variability on dissolutional growth of fissures is investigated on the basis of two‐dimensional numerical simulations. The logarithm of the fissure aperture before dissolution begins is modeled as a Gaussian stationary isotropic random field. The initial phase of dissolutional growth is studied up to the time when turbulent flow first occurs at a point within the fissure (the breakthrough time). The breakthrough time in variable aperture fissures is smaller than that in uniform fissures and decreases as the coefficient of variation of the aperture field (σ/μ) increases. In comparing uniform and variable aperture fissures in limestone, the breakthrough time with σ/μ=0.1 is about a factor of 2 smaller than that in a uniform fissure. The breakthrough time is reduced by about an order of magnitude with σ/μ=2.0. The mechanism leading to reduced breakthrough times is the focusing of flow into preferential flow channels which are enlarged at a faster rate than the surrounding regions of slower flow. Dissolution channels are narrower and more tortuous as σ/μincreases. Investigations of the influence of reaction rate reveal that the influence of aperture variability is more pronounced in rapidly dissolving rock. In uniform fissures in rapidly dissolving minerals, breakthrough times are very long since water becomes saturated with respect to the mineral within a short distance of the entrance to the flow path. However, in variable aperture fissures, breakthrough occurs rapidly because of selective growth along preferential flow channels, which progressively capture larger fractions of the total flow. These results partly explain why conduits develop rapidly in gypsum, although previous one‐dimensional studies suggest that conduit growth will not occur.

Using chemical and physical parameters to define the quality of karstic freshwaters (Timavo River, North-eastern Italy): a chemometric approach

The Timavo River, rising in Monte Nevoso (Slovenia), sinks into a limestone fissure and proceeds subterraneously toward the Adriatic Sea, feeding many springs and ponds in the Karst region near Trieste (Italy). In order to characterize and discriminate the freshwaters of this complex hydrological system, 84 samples were taken in 14 selected sites during the autumnal flood. Six chemical-physical parameters were determined: temperature, pH and conductivity in situ; chloride, nitrate and sulphate contents in the laboratory, by high-performance ion-exchange chromatography (HPIEC). Univariate analysis of dispersion and centrality estimates of the populations of the experimental data allow us to discriminate a group of typically-karstic springs situated near S.Giovanni di Duino, as well as a group—to the north—of “mixed waters” that receive run-off from the northern Isonzo and Vipacco river-beds, and also seem affected by seasonal conditions. The multivariate cluster analysis (CA) confirms the discriminating ability of the considered parameters, and allow us to observe occasional intrusions of waters belonging to a group within a different group. The principal component analysis (PCA) supports the results of CA and permits us to assert the existence of a common watershed for the examined karstic freshwaters, which are characterized by 2 PC's: the ionic solutes are associated with the first component, whereas temperature and pH are associated with the second one. Factor scores show seasonal and meteorological effects on the chemical composition of the freshwaters.

Principles of Early Development of Karst Conduits Under Natural and Man‐Made Conditions Revealed by Mathematical Analysis of Numerical Models

Numerical models of the enlargement of primary fissures in limestone by calcite aggressive water show a complex behavior. If the lengths of the fractures are large and hydraulic heads are low, as is the case in nature, dissolution rates at the exit of the channel determine its development by causing a slow increase of water flow, which after a long gestation time by positive feedback accelerates dramatically within a short time span. Mathematical analysis of simplified approximations yields an analytical expression for the breakthrough time, when this happens, in excellent agreement with the results of a numerical model. This expression quantifies the geometrical, hydraulic, and chemical parameters determining such karst processes. If the lengths of the enlarging channels are small, but hydraulic heads are high, as is the case for artificial hydraulic structures such as dams, it is the widening at the entrance of the flow path which determines the enlargement of the conduit. Within the lifetime of the dam this can cause serious water losses. This can also be explained by mathematical analysis of simplified approximations which yield an analytical threshold condition from which the safety of a dam can be judged. Thus in both cases the dynamic processes of karstification are revealed to gain a deeper understanding of the early development of karst systems. As a further important result, one finds that minimum conditions, below which karstification cannot develop, do not exist.

Dynamics Of Karstification: A Model Applied To Hydraulic Structures In Karst Terranes

To model the development of karst channels from primary fissures in limestone, a computer simulation of solutional widening of a fracture by calcite agressive water is proposed. The parameters defining the problem are the initial width a0 of the fracture, its length l, and the hydraulic gradient i driving water through it. The dissolution rates limestone determine how fast enlargement of the fractures proceeds. At a calcite concentration, c, far from equilibrium, the dissolution follows a first-order rate law, F(1)=α0(ceq-c); close to the equilibrium concentration, ceq, a slow fourth-order rate law F(4)=β0(ceq-c)4 is valid. The results show that, at the time of initiation, the water flow through the karst channels increases slowly in time until an abrupt increase occurs. After this moment of breakthrough, the channel enlarges rapidly and evenly over its entire length by first-order kinetics. Breakthrough times have been calculated for karstification under natural conditions for low hydraulic gradients as functions of a0, l, and i. Special attention is given to karstification in the vicinity of hydraulic structures where hydraulic gradients are high (>0.5) and channel lengths are below 200 m. We find that the breakthrough event will occur in less than 100 years, if: (i/l) > (5.3·10−8a0 −2.63PCO2 −0.77) where l is in m and a0 is in cm, (i/l) is given in m-1, and PCO2[atm] is the CO2 pressure of the water entering the fracture. After this event, the channels will widen to a width of about 1 cm within only 10 years, which can cause considerable leakage near or through hydraulic structures. Finally, critical values of the parameters i, l, a0, which give the conditions of failure in various types of hydraulic structures are discussed.

Fossil vertebrates from Antigua, Lesser Antilles: Evidence for late Holocene human-caused extinctions in the West Indies

Vertebrate remains recovered from a limestone fissure filling on Antigua, Lesser Antilles, are associated with radiocarbon dates ranging from 4300 to 2500 yr B.P., contemporaneous with the earliest aboriginal human occupation of the island. Nine taxa of lizards, snakes, birds, bats, and rodents (one-third of the total number of species represented as fossils) are either completely extinct or have never been recorded historically from Antigua. These extinctions came long after any major climatic changes of the Pleistocene and are best attributed to human-caused environmental degradation in the past 3500 yr. Such unnatural influences have probably altered patterns of distribution and species diversity throughout the West Indies, thus rendering unreliable the data traditionally used in ecological and biogeographic studies that consider only the historically known fauna.

Zinc-lead skarns of the Yeonhwa-Ulchin District, South Korea

The Yeonhwa I, Yeonhwa II, and Ulchin mines, producing 13.5 million metric tons of ore in the period 1962 to 1981, account for 80 percent of South Korea's Zn and Pb production. These skarn deposits occur in basal Cambrian limestone (locally dolomitic) overlying slate, quartzite, and Precambrian granitic basement, and they are the result of hydrothermal activity associated with felsic calc-alkaline plutonism of Late Cretaceous to early Tertiary age.Skarn at Yeonhwa I consists of pipes of pyroxene (+ or - garnet) at depth branching to veins of rhodocrosite-pyrite near the surface in an area of sparse quartz-porphyry dikes. In contrast, skarns at Yeonhwa II and Ulchin display higher garnet/pyroxene ratios and occur as stratabound lenses and irregular masses at or near contacts with larger bodies of quartz monzonite. Exoskarns are zoned in the sequence garnet-pyroxene-(pyroxenoid)-marble relative to slate-limestone contacts or fissures in limestone. The lack of zoning relative to igneous contacts and the presence of porphyry-limestone contacts without skarn indicate that skarn-forming fluids did not originate from magma at the present level of exposure.Electron microprobe analyses reveal that calc-silicates are notably enriched in Mn and Fe. Garnets are intermediate grandite-andradite with 1 to 5 mole percent spessartine. Calcic rhodonite is characteristic of endoskarns and garnet zones, whereas a more calcic pyroxenoid, manganoan bustamite, occurs in pyroxene skarn. Pyroxenes are manganoan salite-ferrosalite; average Fe/Mn ratio (and mole % hedenbergite) in pyroxene decreases from 5.7 (65%) at Ulchin, to 3.5 (59%) at Yeonhwa II, to 1.6 (30%) at Yeonhwa I. This ratio also decreases with distance from garnet zones and correlates with an increase in Mg, suggesting a progressive depletion of Fe in solution due to precipitation of iron-rich garnet near channelways, and a progressive enrichment in Mg in the fluid as it approached equilibrium with dolomitic wall rocks. Based on this and the geologic setting, Ulchin is the most proximal and Yeonhwa II the most distal skarn in terms of distance from their sources of fluids.Pyrrhotite, accompanied by sphalerite, lesser galena, and minor chalcopyrite, are concentrated in pyroxene zones variably altered to chlorite, Mn-rich clays, calcite, quartz, and fluorite. Pyroxene compositions indicate that the maximum oxidation-sulfidation state that could have been imposed on the ore fluid by early skarn was located near the pyrrhotite-pyrite-magnetite buffer. Only the hedenbergitic skarn at Ulchin lay below this buffer and could have controlled the precipitation of pyrrhotite rather than pyrite. Ulchin also contains the district's highest grades of Pb + Zn in skarn, suggesting that reduction of aqueous sulfate by ferrous iron was an important factor in ore deposition. Later ore fluids, and fluids that reached beyond skarn in the most distal deposit, envolved to higher sulfidation states, as demonstrated by pyrite-rhodochrosite veins that cut skarn and pyrrhotite ore, and by the near-surface pyrite-sphalerite-galena-rhodocrosite veins in limestone overlying skarn pipes at Yeonhwa I.

The subfossil deposits of Paryphanta (Mac's Quarry) Cave, Waitomo

Abstract The stratigraphy and sedimentology of the fluvial deposits of a limestone fissure cave in the Waitomo district, western North Island, are described. A microflora, from 60 cm depth and possibly of Otiran age, indicates the former presence of lowland mixed broadleaf-podocarp forest. Faunal remains, found only in the uppermost 25 ern of the deposits, are probably no older than Holocene. Every member of the fauna, comprising 14 species of land bird, a skink, at least one species of frog and 13 species of land snail, inhabited forest. Fewer than half the bird species represented in the subfossil deposits currently inhabit the area, owing primarily to human clearance of indigenous forest. Three species, Notornis mantelli, Strigops habroptilus and Notiomystis cinca, now have exceedingly reduced distribution, and two others, Fulica chathamensis and Megaegotheles nooaezealandiae, are extinct.

Hamakita Man and the Site of Nekata Limestone Quarry at Hamakita

As compared with the remarkable progress of the study of the pre-ceramic culture, the knowledge of Pleistocene man in Japan has been deficient. This may be explained by the fact that most of the pre-ceramic sites so far discovered are open-sites in the loam, which are not suitable for preservation of skeletal remains, and that most of skeletal remains of Pleistocene man, as were found at the sites of Ushikawa, Mikkabi and Kuzuu, are mere fragments occurring in the deposits in the limestone fissures, having been transported and laid by water. The site of Nekata, where the Hamakita man was found, is one of such fissure deposts.The site of the Nekata limestone quarry (Maruhon Co.) at Hamakita is located 16km. north-northeast of Hamamatsu City, Central Japan, and 22km. away from the Pacific Coast (Fig. I-1). The site is situated on the southern border of hills sloping down to a plane which is cultivated into rice field (Figs. I-2 and I-11). The quarry is working to Palaeozoic limestone having caves and fissures which are filled with fossiliferous Pleistocene deposits. Plans of the quarry in which the site is located are shown in Figs. I-3-5 and its birdseyeview in Fig. I-12.The present paper deals with the result of the surveys and excavations of the site performed between 1960 and 1963. In the course of five surveys carried out between 1960 and 1962, several fragments of human bone were obtained with many mammalian fossils as follows (cf. Figs. I-3-5): skull, hip bone and ulna at Locality C ; humerus and clavicle at Locality D ; tibia at Locality B ; Lower molar at Locality D. From June to August, 1962, excavation was made in the Main Cave (Areas I, II and III in Fig. I-5) at the site, for the purpose of obtaining mammalian fossils as many as possible and clarifying the situation of the Pleistocene deposits so as to determine the geologic age of the site (Figs. I-8 and I-9). In June, 1963, excavation was made at another cave (Area IV in Fig. I-4) for the same purpose.

A Liasso-Rhaetic flora in South Wales.

A fossil flora is described from clay-filled fissures in the Carboniferous Limestone near Bridgend, South Wales. Nearly all the specimens belong to the conifer Cheirolepis muensteri . Most of them are charred fragments of various organs in which internal tissues are preserved. Cheirolepis was previously known from compressed German specimens yielding cuticles but no other tissues. The leaf is found to have a single vascular bundle and the wood is of somewhat Taxodiaceous structure but without xylem parenchyma. The bark produces thin scales of secondary phloem and cork. The male cone bears microsporophylls spirally; they are essentially dorsiventral and probably bear two pollen sacs only. The pollen is of unusual structure. The seed is orthotropous and the testa appears to be double. Other species are rare fragments of cuticle representing several Mesozoic genera and isolated spores, three of which have been determined. The age of the flora is between Rhaetic and Lower Liassic; it most resembles a flora in south-west Germany which is regarded as Lias α . Reasons are put forward for supposing that the forest or scrub was burnt, and then the charred fragments were washed into water­courses in limestone fissures which soon after were submerged by the rising Liassic sea.