306 
WILLIAMSON : JOHN WILLIAMSON. 
a similar intermingling of cretaceous and Tertiary organisms occurs 
in the Mgestricbt deposits. . Both these examples indicate transitions 
from one geological epoch to another ; so at Speeton and its 
neighbourhood, we pass from the Oolitic to the Cretaceous formations 
without any break in the continuity of a local submarine deposit of 
blue mud. The fossils afford the sole indications of differences of 
age, and ofthe transition from the Cretaceous to the Oolitic beds. 
Still more important was the discovery of the celebrated plant- 
bed at Gristhorpe bay, now known to be a local estuarian deposit 
intercalated between the marine beds of the upper series of the 
lower Oolites. 
Previous to this discovery, many fine fossil plants, chiefly Cycads, 
Ferns and Equiseta, had been found, in a similiar estuarian deposit, 
in a yet lower part of these Oolites between "Whitby and Scarbrough. 
Amongst these plants a few of the singular objects now constituting 
the genus Williamsonia, had already been noticed.* But prior to 
the Gristhorpe discovery, our knowledge of the Oolitic flora from 
any part of the world was extremely scanty. 
In addition to the north Yorkshire beds just referred to, a few 
Ferns and Cycads had been met with at Bornholm and Mamers on 
the continent, and at Stonesfield and Portland, in England. The 
Gristhorpe deposit alone added more than fifty new species to the 
Oolitic flora. The exact share of credit severally due to Bean and 
Williamson for the discovery of the Gristhorpe beds is not certain, 
but the probability is that it was about equal. The labour of their 
subsequent exploration was equally divided. These discoveries 
brought my father into correspondence with Mr. Adolphe Bronghiart, 
the distinguished author of the " Vegetaux Fossiles," who at once 
signified his estimate of their value by attaching the name of 
Williamsonis " to four of the most striking of the newly discovered 
plants. I 
The portion of my father's life referred to in the last few pages, 
was that in which he was especially brought into contact with the 
late Professor Phillips. I have already referred to the estimate 
* Young & Bird, plate 2, fig. 6, and plate 3, fig. 7. 
t Prodrome d'une Histoire des Vegetaux Fossils, pp. 50, 57, 83 & 95, 1828. 
