282 RAMBLES OF A GEOLOGIST. 



had to yield to the rain above and the mud beneath, and to 

 return to do in Elgin what cannot be done equally well in 

 almost any other town of its size in Scotland, pursue my 

 geological inquiries under cover. 



On this, as on other occcasions, I was struck by the com- 

 plex and very various forms assumed by the ganoid scales of 

 the Wealden. Throughout the Oolitic system generally, in- 

 cluding the Lias, there obtains a singular complexity of type 

 in these little glittering tiles of enamelled bone, which con- 

 trasts strongly with the greatly more simple style which ob- 

 tained among the ganoids of the Palaeozoic period. In many 

 of these last, as in the Coelacanth family, including the ge- 

 nera Holoptychius, Asterolepis, and Glyptolepis, in all their 

 many species, with at least one genus of Dipterians, the 

 genus Dipterus, the external outline and arrangement of 

 scale was as simple as in any of the Cycloid family of the 

 present time. Like slates on a roof, each single scale covered 

 two, and was covered by two in turn ; and the only point of 

 difference which existed in relation to the laying down of 

 these massy slates of bone, and the laying down of the very 

 thin ones of horn which cover fish such as the carp or salmon, 

 was, that in the massier slates, the sides, or cover, nicely 

 bevelled, in order to preserve an equability of thickness 

 throughout, were so adjusted, that two scales at their edges, 

 where they lay the one over the other, were not thicker than 

 one scale at its centre. Even in the other ganoids, their 

 contemporaries, such as the Osteolepis and Diplopterus, where 

 the scales were ranged more in the tile fashion, side by side, 

 there was, with much ingenious carpentry in the fitting, a 

 general simplicity of form. It would almost appear, how- 

 ever, that ere the ganoid order reached the times of the Weald, 

 the simple forms had been exhausted, and that nature, ab- 

 horring repetition, and ever stamping upon the scales some 

 specific characteristic of the creature that bore them, was 



