732 MR. W. S. GRESLEY ON CONE-IN-CONE IN THE [Nov. 1 894, 



that explanation ; and as my illustrations of inverted cone-in-cone 

 were, in effect, slighted by Mr. Young, the next thing to be done, 

 in order to positively demonstrate the existence of inverted cones, 

 was, if possible, to discover such specimens of the formation as 

 could be photographed in situ. There could then be no possibility 

 of error of observation, nor any room left for doubt that the conic 

 masses were not bent or curled round so as to bring the originally 

 flat cone-in-cone upside down upon the under side of the containing 

 rock or nodule. Mr. Young wrote 1 : — " Since my paper was 

 printed in 1886, I have obtained many other illustrative specimens 

 from our Scottish coalfield. These clearly show that the radiation 

 and inversion of the cones, in nodular masses, was due to after- 

 secondary causes, the cone structure being first, the formation 

 of the nodules being second, and the amount of radiation, and 

 inversion of the cones, affords a measure of evidence as to the 

 amount of contraction that has taken place amongst these nodules 

 previous to complete solidification." Why Mr. Young did not supply 

 a good illustration of a typical sample of one of these curiously- 

 inverted cone-in-cone-bearing nodules we were not informed;, 

 perhaps he will favour us with one after he has seen this paper, so 

 that they may be compared with the specimens herein described. 



2. Typical Inverted or Double Cone-in-cone, in the Portage 

 Flags, Pennsylvania. 



In 1890 the present writer came to reside at Erie, Pa., and it rather 

 curiously happened that this very locality, which is situated on Lower 

 Carboniferous or Devonian (?) strata, was a noted one for cone-in- 

 cone. 2 Moreover, I was furnished with a copy of a paper on the 

 Erie cone-in-cone, written in 1880, by Dr. T. D. Ingersoll of that 

 city, whose valuable aid in discovering specimens and working up 

 the subject I have pleasure in acknowledging here. The cone- 

 structure is very prevalent in North-western Pennsylvania ; it 

 occurs on the horizon of a very persistent bed of limestone, 

 called the Eerriferous Limestone. This is a stratum usually several 

 feet thick ; but almost always, when and wherever it thins down 

 to about 4 inches or less, the cone-in-cone formation has been 

 developed in it and the limestone is quite earthy. But it is several 

 hundred feet deeper in the series that the formations which constitute 

 the subject of this paper are met with. 



The typical cone-in-cono in the vicinity of Erie occurs at several 

 more or less definite horizons in the Portage series. These rocks 

 lie almost horizontally, cropping out boldly in cliffs of moderate 

 elevation all along the southern shore of Lake Erie for 80 or 90 

 miles, and as the coast is cut into every few miles by streams enter- 

 ing the lake through ravines, excellent opportunities are afforded of 



1 Geol. Mag. 1892, p. 279. 



2 Pennsylv. 2nd Geol. Surv. Report, Q4 (1881), p. 291. 



