* Welsh Basin, a basin during the Cambrian, Ordovician and Silurian geological periods

He is best known for pioneering faunal analysis of Silurian beds by means of index fossils, especially graptolites, and his proposal ( eventually adopted ) that the beds between the Cambrian beds of north Wales and the Silurian beds of South Wales should be assigned to a new geological period: the Ordovician.

It is composed of the Lockport geological formation of Silurian age, and is similar to the Onondaga geological formation, which runs parallel to it and just to the south, through western New York and southern Ontario.

It is also a rare example in Europe of an outcrop representing three geological time periods ( the Silurian, the Devonian and the Upper Carboniferous ).

The chief geological investigation of the last decade of his life was devoted to the Highlands of Scotland, where he wrongly believed he had succeeded in showing that the vast masses of crystalline schists, previously supposed to be part of what used to be termed the Primitive formations, were really not older than the Silurian period, for that underneath them lay beds of limestone and quartzite containing Lower Silurian ( Cambrian ) fossils.

Today, in Ontario, the Escarpment contains more than 100 sites of geological significance including some of the best exposures of rocks and fossils of the Silurian and Ordovician periods ( 405 to 500 million years old ) to be found anywhere in the world.

The rock strata date from the Prídolí Epoch of the Silurian ; the exceptional exposure here and on the adjoining Albion Sands have resulted in the location's inclusion in the Geological Conservation Review as a candidate for protection as a geological site of special scientific interest ( SSSI ).

The site was a geological ' sandwich ' of basalt in the arch area, Silurian mudstone bedrock in the lower half, and silt in the middle, which precluded the construction of the lower and upper platforms as separately driven tunnels.

* A regional stage in the Silurian geological period.

In geological terms, the Southern Uplands consist mainly of Silurian deposits laid down from 400-500 million years ago and pushed up from the sea bed into an accretionary wedge by the collision of ancient continents.

* Stockdale Shales ( Skelgill beds ), The Lake District, a Silurian period geological formation ; part of the Llandovery Group

It's named for the Silurian geological period because of rocks found there.

He also conducted extensive research on fossils found in the Devonian and Silurian geological strata of the Baltic regions.

In the 1840s fossils of brachiopods and trilobites from the Silurian period were discovered at Woolshed Creek near Duntroon.

The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416. 0 ± 2. 8 Mya ( million years ago ), to the beginning of the Carboniferous Period, about 359. 2 ± 2. 5 Mya.

Lapworth, recognizing that the fossil fauna in the disputed strata were different from those of either the Cambrian or the Silurian periods, realized that they should be placed in a period of their own.

The Ordovician and Silurian periods were warm greenhouse periods, with the highest sea levels of the Paleozoic ( 200 m above today's ); the warm climate was interrupted only by a ~ 30 Ma cool period, the Early Palaeozoic Icehouse, culminating in the Hirnantian glaciation.

Xylem cells are specialised for conduction of water, and first appeared in plants during their transition to land in the Silurian period more than 425 million years ago ( see Cooksonia ).

The Silurian is a geologic period and system that extends from the end of the Ordovician Period, about 443. 7 ± 1. 5 million years ago ( mya ), to the beginning of the Devonian Period, about 416. 0 ± 2. 8 mya.

The oldest known scorpions lived around 430 million years ago in the Silurian period, on the bottom of shallow tropical seas.

The oldest generally accepted shark scales are from about 420 million years ago, in the Silurian period.

Their numbers began to decline during the middle of the Silurian period, and they became extinct at the end of the Permian period,.

Rugose corals became dominant by the middle of the Silurian period, and became extinct early in the Triassic period.

Immediately above the topmost layer of the marine rock sequence forming Murchison's Silurian period was a thin layer of dark sand containing numerous remains of early fish, especially their scales, along with plant debris, spores and microscopic mites.

This class of arthropod is thought to be among the first animals to have colonised land during the Silurian geologic period.

The later Silurian period saw the creation of limestone and shale, visible along the southern Marloes peninsula.

Neither Tethys oceans should be confused with the Rheic Ocean, which existed to the west of them in the Silurian period.

Reference is occasionally made to this period of Celtic history by the use of terms such as " Silurian ".

The geologic period Silurian was first described by Roderick Murchison in rocks located in the original lands of the Silures, hence the name.

During the Silurian period, some magnesium substituted for some of the calcium in the carbonates, slowly forming harder ( dolomitic ) sedimentary strata in the same fashion.

At lower elevations on the mountain, and stratigraphically below the Littleton Formation, the bedrock is from the Silurian period, consisting of Rangeley Formation schists, Perry Mountain Formation quartzites, the Francestown Formation granulite, and the Warner Formation granulite.

The vertebrate jaw probably originally evolved in the Silurian period and appeared in the Placoderm fish which further diversified in the Devonian.

The vertebrate jaw probably originally evolved in the Silurian period and appeared in the Placoderm fish which further diversified in the Devonian.

The Silurian system was first identified by British geologist Sir Roderick Impey Murchison, who was examining fossil-bearing sedimentary rock strata in south Wales in the early 1830s.

Sir Roderick Impey Murchison, 1st Baronet KCB DCL FRS FRSE FLS PRGS PBA MRIA ( 22 February 1792 – 22 October 1871 ) was a Scottish geologist who first described and investigated the Silurian system.

The result was the establishment of the Silurian system under which were grouped, for the first time, a remarkable series of formations, each replete with distinctive organic remains other than and very different from those of the other rocks of England.

The establishment of the Silurian system was followed by that of the Devonian system, an investigation in which Murchison assisted, both in the south-west of England and in the Rhineland.

The greater portion of the county of Dumfries belongs to the Silurian tableland of the south of Scotland which contains representatives of all the divisions of that system from the Arenig to the Ludlow rocks.

* Sir Roderick Murchison KCB FRS, Scottish geologist who first described and investigated the Silurian system.

* Roderick Murchison-geologist, originator of the Silurian system

Species included in the Naraoiidae are known from the second half of the Lower Cambrian to the end of the Upper Silurian.

It is the longest of the Phanerozoic eras, and is subdivided into six geologic periods ( from oldest to youngest ): the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.

The Silurian Lingula differs but little from the living species of this genus ".

Scorpions have been found in many fossil records, including marine Silurian deposits, coal deposits from the Carboniferous Period and in amber.

The oldest near-complete fossil lobopods date to the Lower Cambrian ; some are also known from a Silurian Lagerstätte.

However, only one species is known from each of the Ordovician and Silurian periods, with a few more known from the Carboniferous ( Mazon Creek ).

Fossil plants with anatomically preserved xylem are known from the Silurian ( more than 400 million years ago ), and trace fossils resembling individual xylem cells may be found in earlier Ordovician rocks.

A banded tube from the late Silurian / early Devonian.

Bands on the walls of tubes, in fact apparent from the early Silurian onwards, are an early improvisation to aid the easy flow of water.

The fiftieth Doctor Who Virgin New Adventures novel Happy Endings by Paul Cornell features a Polari-speaking Silurian musical duo from the 30th century called Jacquilian and Sanki.

For example, the Caledonian Orogeny refers to the Silurian and Devonian events that resulted from the collision of Laurentia with Eastern Avalonia and other former fragments of Gondwana.

* provides a detailed history of a number of orogens, including the Caledonian Oregeny, which lasted from the late Cambrian to the Devonian, with the main collisional events occurring during Ordovician and Silurian times.

Molecular analysis suggests that the hexapods diverged from their sister group, the Anostraca ( fairy shrimps ), at around the start of the Silurian period-coinciding with the appearance of vascular plants on land.

The shallow-water limestones from the Ordovician and Silurian periods of Estonia are famous for echinoids.

The primary mountains within the county ( From west to east: Wills, Evitts, Dunning, and Tussey mountains ) extend from the southern border with Maryland to the northeast into Blair County, and are held up by the Silurian Tuscarora Formation, made of quartz sandstone and conglomerate.

Rosendale natural cement was produced from dolostone extracted from the Rosendale and Whiteport members of the Late Silurian Rondout Formation.

The Paleo-Tethys Ocean, mentioned above, existed from the Silurian ( 440 Ma ) through the Jurassic periods, between the Hunic terranes and Gondwana ( later the Cimmerian terranes ).