FORMATION OF COAL- 203 



One is, that they were washed into great fresh water lagoons, 

 and rapidly covered up with debris, brought down by rivers 

 flowing therein. 



The other theory which I hold to be the correct one, was first 

 propounded by M. J. A. De Luc, F.R.S., in 1793— 9 j. it is, that 

 coal has been formed by the remains of plants which grew in the local- 

 ities where we now find it. This theory has been slightly modified to 

 the extent that vegetation grew at the mouth of a great river, that 

 the land sank below the sea level, and that the debris brought down 

 by the river covered the vegetation and was either deposited faster 

 than the sinking of the land took place, and thus raised it 

 sufficiently above the water for fresh vegetation to grow, or the 

 land must have ceased to sink, or perhaps have been again elevated 

 above the surface. 



We may notice next the size of some of the American coal- 

 fields which are in general much more extensive than those in 

 Great Britain. The Pennsylvania coal-field embraces 20,000 

 square miles. The Illinois coal basin includes Indiana, and West 

 Kentucky, and extends over an area of 51,700 square miles. The 

 Ohio coalfield is stated by Dr. Newbury to cover over 10,000 

 square miles. Others again are much smaller, as the coal fields 

 of Tennissee, said to be 5,100 square miles. 



These great areas we may compare with the areas of modern 

 river-deltas, as it is in such situations we conceive that coal-beds may 

 have been formed. That of the Ganges is 48,404 square miles. 

 The Delta of the Mississippi is larger than that of the Nile ; 

 from the Gulf of Mexico northward for about 100 miles, there is 

 a great dead flat, covered with pine forest, swamps, and 

 marshes ; the river is subject to great floods during the spring 

 melting of the snow on the mountains to its north , the water 

 comes down with great rapidity sweeping the trees far into the 

 Gulf, or distributing them over the Delta for hundreds of miles. 

 The carboniferous rivers were subject to similar floods as shown by 

 the black layers of decayed vegetation so common in the rocks 



