144 Mr. Prestwich on the Structure of 



same fishes with imperfect vegetable impressions, occur occasionally in the 

 underlying- bed of micaceous shale. 



In the subjacent, red, micaceous sandstones, alternating with beds of con- 

 glomerate, fragments of the same fishes are also found ; and it is only w here 

 these sandstones are entirely replaced by the conglomerates, that the fish 

 exuviae disappear. This absence might be expected, from the fragmentary 

 nature of the deposit, which must have been accumulated by a body of water 

 possessing great velocity and transporting power ; and the friction of such 

 numberless masses of rolled rocks, must have destroyed any animal or vege- 

 table remains thrown amongst them. As we ascend in the series we have 

 indications of alternating periods of comparative calm, during which the finer 

 sandstones were deposited. As these periods increased in duration, the more 

 favourable became the condition of the water for the existence of animals, 

 until at last, during the slow and gradual deposition of the grey clay stratum, 

 the entombed reliquias indicate an epoch, when the waters probably possessed 

 but little velocity. This temporary calm was followed by another paroxysm, 

 by which the shales and clay were covered to a great thickness with a friable, 

 brecciated mass. This breccia forms the highest bed of the deposit in the 

 district, and caps the hill upon which the small hamlet of Findon is built. 



Trap Rocks. 

 A dyke of trap appears on the coast, near the junction of the red sandstone 

 ind the slate rocks not far from Gamrie church (see PI. X. Sect. 2.), and 

 ranges inland in a southerly direction. It is composed of a sienitic green- 

 stone, and is from twenty to thirty feet across. 



At Castle Hill, Gamrie, and at several other places in the same neighbour- 

 hood, and also on the schistose cliffs between Banff and Blackpots (see 

 PI. X. No. 4.), a dark-coloured tenacious clay, containing a few, subordinate 

 beds of a light yellow sand, reposes almost horizontally upon the other rocks. 

 I have been informed that lias fossils are found in this deposit*. 



* In the paper originally read before the Society, this deposit was described as lias upon the 

 authority of geologists in that country. — See Proceedings, vol. ii. No. 40. page 187, March, 1837- 

 See for a correction of this statement the Appendix to the paper, p. 1 46. 



