part 4] JURASSIC CHEOJs^OLoaY. 395 



Edward Wilson found, in the Junction-Bed of the Dorset coast 

 some 25 years ago, when in company with Mr. Tutcher, a similar 

 species: the specimen is now in the Bristol Museum. Accompany- 

 ing my example were some unfamiliar Harpoceratoid ammonites 

 which will require further investigation. This bed possibly 3delded 

 those Dactyliocerates, of about Transition-Bed date, which have 

 been obtained from the Dorset coast. ^ 



We may now return to Mliynclionella houcliareli : three or four 

 examples can sometimes be obtained from a small lump — from 

 rock which belongs to the base of the Upper Lias : that is to 

 say, it is to be sought for in the blocks immediately above the 

 Marlstone, which is congruous with Moore's post-Saurian-Bed 

 position. It also comes from the Watton Bed, from Ilminster, 

 South Petherton, and other places. It is a form of fairly wide 

 distribution : Thomas Davidson figures an example from Cromarty 

 (Scotland) ; Eudes-Deslongchamps mentions it from Normandy. 

 But all mention and figures of it are not to be trusted. I seem to 

 recollect the name being applied to some figured examples which 

 have nothing to do with Davidson's species. And I have my doubts 

 about the Cromarty shell. 



The widespread occurrence of strata with Rhynchonella hoio- 

 chardi indicates a period of perhaps greater quiescence after their 

 deposition than had been the case with some previous deposits. 

 But the houchardi deposit did not escape wholly, for there are 

 some large areas without it — I think that the Cotteswolds might 

 be cited ; and in some cases where Hh. houchardi is found, it has 

 certainly been taken from its own bed and redeposited. 



It is from such evidence as this — some of it particularly frag- 

 mentary — that a reconstruction of the course of events in the 

 matter of deposition had to be made. 



The Dorset coast, then, seems to supply evidence, by fossils and 

 sometimes by fragments of strata, for the following sequence : — 



(6) Harpoceras-falciferum Bed. 

 (5) Rhynchonella-bouchardi Bed. 

 (4) Dactylioceras-athleticum Bed. 

 (3) Rhynchonella-serrata Bed. 

 (2) PleiiTotomaria Bed. 

 (1) Spinatum Bed. 



(C) The Middle Lias (Domerian) of Thorncombe Beacon. 



As the Junction-Bed of Watton Cliff contains Domerian strata 

 of earlier date than those found in the bed under the Western 

 Cliffs, it becomes necessary to give a short summary of these 

 deposits. The information is required for several reasons, as will 

 be seen later. 



Blocks and pebbles scattered along the shore from under Thorn- 

 combe Beacon to Ejqjesmouth show various matrices, and con- 

 tain many different fossils. In fact, some of the small pebbles 



1 I, 5, p. 83. 

 Q. J. a. S. No. 312. 2 E 



