250 
THE GEOLOGIST. 
The Portland Ossiferous Fissures. 
SiE, — The Eev. T. Allen's letter on the Portland fissures in your last 
number, induces me to send you a second communication upon that 
question. I have visited Portland during the present month, and de- 
scended one of the fissures, in which a large number of bones were found 
some mouths ago by a warder of the name of Maddock. I obtained all 
the information I was able from Mr. Maddock on the subject, and saw 
most of the bones. They are deposited in the Grovernment Office at the 
Vern Fort. Lieutenant Home, E.E., was kind enough to allow me to 
examine them thoroughly, and gave me much information and assistance 
in investigating the phenomena of the gullies. 
I must premise that I did not examine any gullies in that portion of 
the island where the Portland beds are overlaid by the Lower Purbeck 
calcareous shale. 
I saw at a glance that the 
explanation I offered in a for- 
mer communication to your 
Journal was incorrect. Shrink- 
ar/e will not account for these 
Sea-level ^ssures. They appear to arise 
^^■ T o -L • XI- n ii 1 ^ from a ponderous stone-struc- 
Jig. 1. — Section showing the Portland fissures. , , • j i 4- ^„ 
^ . n 1 I J 1 u 1 1 ture bemar raised bv nature on 
stone, fissured ; 6, sand}' clay : shaly clav. i i r. i ^• 
• a bad foundation. 
They extend as nearly as possible in the direction of the length of the 
island ; and are possibly connected with the last great movement, which 
affected the configuration of that part of the coast. This movement seems 
to have been posterior to the outspread of gravel on the heights to the 
north of the Ridgway fault : for the elevated beds to the south of the 
fault are bare of gravel. 
On the west side of the northern end of Portland the beds are much 
broken and tumbled seawards, the gullies being very numerous. Slips 
occur on this side of the island. On" the whole, I conclude that Portland 
is the remnant of an oblong mass of strata brought into its present position 
by the disturbances alluded to. Tliere is a very curious miniature model 
of the island between Upwey and Bincombe, "formed by the combined 
effects of faulting and denudation, and in the same series of beds that 
occur at Portland itself. 
The general structure of the gullies 
seems to be due to a slip of such a 
kind that they are more open at the 
bottom than at the top. (Fig. 2.) 
One side has usually slightly sunk 
a foot or so. The jagged edges of 
broken stones and flints correspond 
on the t wo sides of the fissure. The 
rock seems a good deal shaken on 
, . p both sides of the larger fissures. 
Fig 2.-Ideal section showing nature of ^yi^j^ j question of the 
slip of beds m forming a fissure: a b, ^^^^^^^ ^- or closed at the 
masses of stone-rock subsiding on the top, the abovS description of them will 
unequaily-yieldiug bed of saudv clav, c. i . .^ i i xi x i 
^ . . ' show that, on the whole, they tend 
to be closed. Yet they are not so entirely. Often they seem to be roofed 
by fragments that have fallen in from their sides, and have got jammed, 
and subsequently smaller fragments and rubbish have accumulated upon 
