290 MK MILNE ON THE MID-LOTHIAN AND EAST-LOTHIAN COAL-FIELDS. 



rivers flowed, charged witli the spoils of the diy land ; — and that these rivers 

 were of great depth and magnitude, is obvious from the number and size of the 

 trees which they transported. 



It is impossible, therefore, to assume, that the waters in which the coaly ve- 

 getables floated and sunk were free from cmrents, — and currents of very con- 

 siderable force. It is true that these cm-rents may have been more powerful at 

 one time than at another. When any great inundation took place, whereby im- 

 mense quantities of vegetable matter were swept from the plains and marshes, 

 the currents would be greatest ; — and then there would be immediately a deposi- 

 tion, first of sandstones and next of shales. It would be some time before the ve- 

 getable masses would sink ; and undoubtedly the waters would then have attained 

 a more quiescent state. But still, unless it be supposed that the rivers were at 

 times altogether dried up, there must have been currents to interfere greatly 

 with the equal distribution of the vegetable matter. 



Such would be the case, even on the supposition that the waters which co- 

 vered the district were entu-ely fresh-water, and not subject to the action of the 

 tides. But this would be a supposition far more favourable than the facts war- 

 rant. The existence of shells and zoophytes, undoubtedly marine, in beds of 

 shale* and limestone, which occm- in the lower half of the deposit, proves in- 

 contestibly, that the waters were at that period entirely salt, and therefore pro- 

 bably subject to oceanic tides. This circumstance, therefore, must be taken into 

 account in considering the whole question. 



I may here observe, that whilst the waters which covered the district were, 

 during the deposition of the lower half of the strata, of decidedly marine character, 

 they were latterly, in all probability, mixed with a larger proportion, if they did 

 not entirely consist, of fresh water. It wUl be remembered, that it is in the upper 

 series of coals that the two species of Unio occur, forming a bed extending for 

 many miles. This change of character in the waters, is precisely what would be 

 expected, if there were rivers which, either incessantly or periodically, spread 

 over the bottom of the estuaiy large supplies of sedimentary matter. The bot- 

 tom, as it rose in level, would gradually push back the sea, and thus alter the 

 proportions of salt and fr-esh water, till little of the former remained. From 

 this, another effect would follow, viz. the greater influence of currents, ai-ising 

 from the river-floods, so that in the upper part of the deposit we ought to find 

 greater irregulai'ity in the thickness of all the strata. Tins inference agrees 



* In the shale which forms the roof the Rough or Kailblades coal at Bryants (situated about 25 fa- 

 thoms above the North Greens coal), I have found a species of Lingula in great abundance. It appears 

 to belong to a species undescribed. It resembles most the Lingvla Beanii. (Phillip's Yorkshire, i. 128.) 

 In the shale which forms the roof of a coal-seam near Rutherford Inn, (in the parish of Linton), I have 

 tound iunumerable remains of the Producia costata (Phillh's), with the spines well preserved. The 

 coal-seam is double, — the upper pait being l(j inches thick. 



