178 THE CRUISE OF THE BETSEY ; OR, 



I was struck, during my explorations at this time, as I had 

 been often before, by the style of grouping, if I may so speak, 

 which obtains among the Lower Old Red fossils. In no de- 

 posit with which I am acquainted, however rich in remains, 

 have all its ichthyolites been found lying together. The col- 

 lector finds some one or two species very numerous; some 

 two or three considerably less so, but not unfrequent ; some 

 one or two more, perhaps, exceedingly rare ; and a few, though 

 abundant in other localities, that never occur at all. In the 

 Cromarty beds, for instance, I never found a Holoptychius, 

 and a Dipterus only once ; the Diplopterus is rare ; the Glyp- 

 tolepis not common ; the Cheirolepis and Pterichthys more 

 so, but not very abundant; the Cheiracanthus and Dipli- 

 canthus, on the other hand, are numerous ; and the Osteo- 

 lepis and Coccosteus more numerous still. But in other 

 deposits of the same formation, though a similar style of 

 grouping obtains, the proportions are reversed with regard to 

 species and genera : the fish rare in one locality abound in 

 another. In Banniskirk, for instance, the Dipterus is ex- 

 ceedingly common, while the Osteolepis and Coccosteus are 

 rare, and the Cheiracanthus and Cheirolepis seem altogether 

 awanting. Again, in the Morayshire deposits, the Glypto- 

 lepis is abundant, and noble specimens of the Lower Old Red 

 Holoptychius of which more anon are to be found in the 

 neighbourhood of Thurso, associated with remains of the Dip- 

 lopterus, Coccosteus, Dipterus, and Osteolepis. The fact may 

 be deemed of some little interest by the geologist, and may 

 serve to inculcate caution, by showing that it is not always 

 safe to determine regarding the place or age of subordinate 

 formations from the per centage of certain fossils which they 

 may be found to contain, or from the fact that they should 

 want some certain organisms of the system to which they be- 

 long, and possess others. These differences may and do exist 

 in contemporary deposits ; and I had a striking example, on 



