V^EIN. 



at Cockfield-fell, is part of the longeft. dyke which has 

 been traced in England, or perhaps in any other country. 

 According to the defcription of it in Mr. Bakewell's In- 

 iroduaion to Geology, " it extends from the weftern fide 

 of Durham in an eaftward direflion, to Bewick in York- 

 fhirc, croffing the river Tees at this place, and proceeding 

 in tlie fame direftion through the Cleveland hills, in the 

 Eaft Riding of Yorkfhire, to the fea-coafl between Scar- 

 borough and Whitby. It rifes to the furface, and is quar- 

 ried, in many parts of its courfe, for ftone to repair the 

 roads. It crolfes the turnpike near the feven mile-ftone 

 from Whitby to Pukering, where there is a quarry funk in 

 it. The vein, or dyke, is here about ten yards wide ; the 

 ftone is a dark greyifh-brown bafalt, and is the principal 

 material for mending the roads in the diilrift called Cleve- 

 land. The extent of this dyke has been traced in a direft 

 line about feventy miles. In its courfe it interfeCls the 

 metalliferous lime-done of Durham, the coal diftridl, and 

 the aluminous fchiftus. The circumftances attending this 

 and other extenfive dykes, which have not hitherto been re- 

 garded by geologifts, completely invalidate," fays Mr. Bake- 

 well, " the theory, that thefe dyk-es were originally open fif- 

 fures, formed by the drying or fhrinking in of the rocks. 

 As the different rock formations through which it pafles 

 contain different organic remains, they mull hgve been 

 formed in fucceffion at different periods, and the metalli- 

 ferous lime, with the lower ftrata, mull have been con- 

 folidated long before the upper ftrata were depofited ; 

 and the caufes which might difpofe the upper ftrata to 

 fhrinkand open, cannot be fuppofed to aft on the lower 

 rocks. It is alfo remarkable, that the width of this vein 

 is more than twenty yards in the lower rocks on the weft ; 

 but in the upper rocks it is not more than ten yards. The 

 dyke muft have been filled with its contents at the time of 

 its formation, otherwife it would contain fragments of the 

 rocks which it interfefts. As it paffes through tlie lime- 

 ftone, it has rendered it more cryftalline in its vicinity, and 

 the effefts in charring the coal, before defcribed, point to 

 fubterranean fire as the original caufe of its formation, and 

 as the fource whence the bafalt that fills it was fupplied. 

 The clofe refemblance between the bafalt and compafl lava, 

 add probability to the opinion that this great dyke was 

 originally formed by an expanfive force operating from 

 below, which opened a chafm in the- furface of the earth, 

 and ejefted the contents in a ftate of fufion. A volcanic 

 dyke was formed on the weftern fide of Vefuvius, June 12, 

 1794, two thoufand three hundred and feventy-five feet 

 in length, and two hundred and thirty-feven feet in breadth, 

 through which lava rofe to the furface. This lava,, when 

 cooled, formed a wall of ftone interfering the former beds 

 of lava, and conftituting a real dyke. The ftone has a dark- 

 grey colour, and is in fome parts fo compaft as to refemble 

 horn-ftone." Si'e Volcano. 



The effefts of bafaltic veins on the contiguous parts of 

 the ftrata of fand-ftone which they interfeft, are no lefs re- 

 markable. In fome inftances, the fand-ftone appears very 

 confiderably indurated, and converted into a fubftance refem- 

 bling horn-ilone. 



It is obferved by Mr. Allan, Tranfaftions of the Royal 

 Society of Edinburgh, vol. vii. that the fand-ftone which is 

 thus indurated, contains calcareous earth, which appears to 

 have promoted its femi-vitrification ; but where the fand- 

 ftone remains unchanged in the vicinity of a dyke, the cal- 

 careous earth is wanting. Sir G. Mackenzie obferved 

 bafaltic dykes in Iceland, the walls or fides of which were 

 lined with a jjhiffy fubftance refembling obfidian. Thefe 

 effects offer further illuftration of the igneous origin of 



bafaltic veins. A very interefting account of the effeiS. 

 produced by bafaltic veins on the different beds of rock at 

 the Giants' Caufeway, and on other parts of the fame 

 range on the north coaft of Antrim, is given in the third 

 volume of the Tranfadlions of the Geological Society. 



Various beds of columnar bai.ilt, argillaceous lime-ftoneJ 

 and chalk, are interfefted by perpendicular dykes or veins! 

 of bafalt. The chalk in the vicinity often undergoes a re 

 raarkable change, extending eight or ten feet from the wal( 

 on each fide, and thence gradually decreafes. The pa 

 iieareft the bafalt is converted into a dark-brown cryftalline' 

 lime-ftone, like coarfe-grained primitive lime-ftone. The 

 next ftate is that of finer-grained primitive lime-ftone, or fac- 

 charine lime-ftone ; then fine-grained arenaceous lime-ftone. 

 A compaft variety, having a porcelain afpett, and a blueifh- 

 grey colour, next fucceeds ; this, towards the outer edge, 

 becomes gradually white, and infenfibly graduates into 

 unaltered chalk. The flints in the altered chalk affume 

 a greyifti-yellow colour. The altered chalk is highly 

 phofphorefccnt when fubjefted to heat. In other parts of 

 the range, the argillaceous beds of lias appear converted into 

 horn-ftone by contaft with the bafalt, and con-tain in that 

 ftate the imbedded foffils peculiar to the lias ftratum. (See 

 Strata.) The bafalt in fome of the veins is columnar; 

 but the columns lie horizontally. It has been conjeftured, 

 with fome probability, that this has been caufed by its 

 paffmg from a ftate of igneous fluidity, and the refrigeration 

 commencing from the fides. From the fame caufe, in the 

 beds of columnar bafalt in that range, (fee Giants' 

 Caufeway,') the columns are perpendicular, the cooling 

 commencing from the top and the bottom of each bed. 

 The marine organic remains in the ftrata over the bafalt, 

 prove that the whole were formed under the fea. In fome 

 inftances, bafaltic veins appear to have been opened, and the 

 intervening fpace filled with debris from the upper ftrata ; 

 and there are bafaltic dykes in Northumberland, in which 

 the bafalt being divided into irregular maffes, the inter- 

 ftices are filled with iron-clay, and contain impreffions of 

 ferns, likethofe in the coal ftrata which thefe dykes or veins 

 interfedt. On the whole, no country in the world which 

 has yet been examined prefents fo many interefting ap- 

 pearances of bafaltic veins as the northern parts of Great 

 Britain and Ireland, nor are they any where expofed to the 

 eye of the obferver with fo much diftinftnefs as on many 

 parts of the fea-coaft, where the ocean has bared the fur- 

 face, and expofed the moft magnificent and inftruftive feftions 

 of entire mountains, penetrated by theie veins to the height 

 of many hundred feet. The veins may often be feen extend- 

 ing from the mountains into the fea, rifing up like enormous 

 waUs, which ferve as monuments of the ravages of the ocean 

 upon the coaft. The great hardnefs of the fubftance which 

 fills the veins has prevented their deftruftion by the waves 

 that have broken down and removed the mountain maffes in 

 which thefe veins were once imbedded. 



Meffrs. Lewis and Clarke, the American travellers, de- 

 fcribe extenfive walls of dark columnar ftone ranging through 

 the interior of North America : thefe walls were undoubtedly 

 dykes or veins of columnar bafalt, remaining where the fur- 

 face of the ground had been waftied away. There are alfo 

 inftances where the fubftance of bafaltic veins has been 

 fofter than the furrounding rock, and is waftied out wherever 

 the rock is expofed, forming deep fiffures, with perpen- 

 dicular walls of rocks on each fide. Such appearances are 

 not uncommon on the fea-coaft in various parts of Scotland. 

 For an account of bafaltic rocks, fee Trap. 



Vein is alfo applied'to t^ie ftreaks, or waves, of divers 

 colours appearing on feveral forts of woods, ftones, &c. 



as 



