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THE GEOLOGIST. 



The Portland Ossiferous Fissures. 



Sir, — The Rev. 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 months ago by a warder of the name of Macldock. 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 Government Office at the 

 Vern Port. Lieutenant Home, R.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- 

 age will not account for these 

 Sea-level. fi ssur es. They appear to arise 

 -p- n „ ... , . , , • „ ,, . , . ' from a ponderous stone-struc- 

 rig. 1. — Section showing the Portland fissures. , , • i • j u + 



a, stone, fissured ; b, sandy day ; c, shaly clay. tu ™ * e ™& TT* hj 

 J J J J 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 Eidgway 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. There 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 two sides of the fissure. The 

 rock seems a good deal shaken on 

 both sides of the larger fissures. 



With regard to the question of the 

 slip or beds in forming a fissure : a, b, /• r • 1 -i j , 



1 e . i k u -j- liT nssures being open or closed at the 

 masses ot stone-rock, subsiding on the , ,i i ° r • , . 

 nnequally-y icldino- bed of sandy clay, e. *?& ^ a ^ e description of them will 

 1 J J e 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 



Fig. 2. — Ideal section showing nature of 



