Solérzano & Hobson—Plant-remains in Basalt, Mexico. 217 
32 feet in the recent shafts) on shafts disused and neglected for cen- 
turies. And of course this expansion, when it became too great for 
stability, would ultimately produce subsidences at the surface such as 
were once visible at A and C. 
It may perhaps seem disappointing, at first, that something 
approximating to the discovery at Eltham in 1878 was not the result 
of the course taken by the recent tunnel beneath the site of the 
subsidence at A. But at Eltham the chamber in the Chalk was pre- 
served because the shaft leading to it was preserved. It had escaped 
destruction through the exceptional circumstances that it had been 
utilized, in some way or other, centuries after the purposes of its 
originators had been forgotten. But in the case of the disused and 
neglected pits at Blackheath, the surface subsidences implied the 
simultaneous destruction of all that had up to that time remained of 
shaft and chamber below. The evidence afforded by the recent tunnel 
therefore confirms, as strongly as circumstances allow, the hypothesis 
that these Blackheath subsidences mark the sites where once existed 
shafts with chambers in the Chalk below, like the pit at Eltham. 
Note. 
This seems to be a good place for the introduction of the following 
brief acount of a Blackheath subsidence in the year 1798. It is from 
the Gentleman’s Magazine for that year, p. 1078 :-— 
“Noy. 19. A singular accident happened last week at Blackheath. 
As a farmer and his son were conversing together in a field where 
a horse was feeding, on a sudden the animal sunk into the earth (hind 
feet first) to the depth of 15 feet, out of which he was dug, crushed 
to death. The cavity was only just sufficient to admit his body, the 
surrounding soil remaining firm.” 
This certainly suggests a subsidence resembling those at A and C. 
But its scene must have been a little east, or north-east, of the 
common now known as Blackheath. 
VI.—Prant Remains in Basatt, Mexico. 
By Dr. M. M. Sorérzano, of the Museo Michoacano, Morelia, Mexico, and 
Bernarp Hoxrson, M.Se., F.G.S., of the University of Manchester. 
(PLATE XI.) 
HEN the members of the ‘‘Jorullo Excursion”! of the Tenth 
International Geological Congress were in the city of Morelia, 
in Mexico, they visited the College of St. Nicholas (founded in 1540), 
in the buildings of which is the Museo Michoacano. One of the most 
interesting objects in the Museum in question is a piece of basaltic 
laya containing remains of maize, which has been described by 
Dr. M. M. Solérzano, the Curator of the Museum, in an article 
entitled “‘ Breve noticia acerca de algunos productos volednicos de las 
immediaciones de esta ciudad” in the ‘ Boletin de la Sociedad 
Michoacana de Geographia y Estadistica,”” Tomo ii, Nam. 8, Morelia, 
Julio 15 de 1906, pp. 59, 60. 
‘ See Gon. Mac., 1907, p. 5. 
