Tlie Carboniferous Formation. 39 



eleven chief seams of coal, one of which is five feet thick ; they 

 are fairly good for burning though rather too hard. Some of the 

 beds of shale which are between these seams of coal are very fossil- 

 iferous, one especially so near Trannent, which contains numerous 

 species of ferns (sphenopteris, etc.), calamites, lepidodendron, and 

 other plants ; and also the remains of some of the large predacious 

 fish of this period. 



In the lower division there are five distinct beds of limestone, 

 each characterized by peculiar fossils, although some of the com- 

 moner species of corals are found in all of them. Between each 

 of these limestones there is a bed of shale, and in one or two 

 instances a bed of sandstone ; these beds of shale and sandstone 

 are also distinguishable by their organic remains. It is perhaps 

 not necessary for our present purpose to describe each of these 

 beds in detail. The limestones are generally characterized by the 

 presence of large patches of corals — one limestone in especial 

 contains five species of corals, three of which occur in it in large 

 patches. The shales contain numerous species of brachiopoda, 

 and sometimes a layer an inch or two thick is completely filled with 

 shells of one species of productus or spirifer. There is one shale 

 which contains six species of lamellibranchiate molluscs, and two 

 gasteropoda, — classes of shells which are, numerically speaking, 

 rare in this formation ; and which, in the section of which we 

 have been speaking, are only found in any abundance in this 

 particular bed. 



This period is important in considering the progressive develop- 

 ment of animals as that in which reptiles make their first appearance, 

 and in which fishes reach their climax. The first discovery of a 

 reptile in the coal was announced in 1844, from a specimen found in 

 Germany. Soon after, in the year 1847, several species of reptiles of 

 a genus named Archegosaurus, were discovered in the same country. 

 The largest species of this class reached three feet in length. They 

 seem to have an intermediate link between the Batrachians and 

 the Saurians. 



The fishes, as we have said, reached during this period their 

 climax; it was there that they attained their greatest magnitude 

 and highest development. They are all characterized by possessing 

 hard bony scales and a cartilaginous skeleton. They had large 

 jaws, measuring in a specimen procured from Gilmerton, near 

 Edinburgh, about two feet, which are filled with teeth. These 

 teeth are of two kinds, — small serial teeth, and a larger one placed 

 at long intervals. A specimen of the latter from the same place 

 measured about three inches in length. They all possessed hetero- 

 cercal tails, that is the vertebral column is produced into the upper 

 branch of the tail. 



