Heilprin.] 54 [Jan. 6, 1888. 
Uhler had here confounded under one name two entirely distinct forma- 
tions of very widely separated ages. The specimen of ‘ Albirupean”’ 
exhibited this evening contains fossils (a brachiopod and encrinite stems) 
characteristic of a Paleozoic and not a Mesozoic formation, and the petro- 
logical character of the rock is also that of an ancient sandstone, resem- 
bling the Medina or Potsdam san@stones. The fossils point to the lower 
Silurian age or thereabouts of the sandstone, and it is probably of nearly 
related age to the metamorphic limestones which occur in the vicinity of 
Baltimore. It is of course incredible that a rock of Paleozoic age could 
overlie the ‘‘Baltimorean’’ clays, and Professor Uhler has given no facts 
or sections to prove that such is the case. 
The mistake has probably arisen in confounding the weathered portions 
of the sandstone with the sands and clays of Mesozoic or more recent age 
which occasionally overlie the variegated, iron-bearing clays. As a result 
of decomposition, the ancient sandstone frequently becomes loose and 
sandy, and is marked with ferruginous streaks so as to closely resemble 
the much more recent sands and clays of the neighborhood. An example 
of this kind may be seen a few miles north of Baltimore. The mistake 
of confounding the two formations would therefore be a very natural one, 
especially as the younger formation is in large part made out of the older 
one, and as outcrops in the region are scarce. Geologists cannot be ex- 
pected to accept the term ‘‘Albirupean ;”’ for even if limited on the one 
hand to the sandbeds of Mesozoic age, or on the other to the patches of 
Paleozoic quartzite, it is, to say the least, unnecessary, while if applied to 
both formations it would be a source of confusion. 
Professor Heilprin stated that: 
From the data and material presented by Dr. Uhler, he was disposed to 
agree with Professor Lewis that two or more very distinct formations 
were included in Uhler’s ‘alluvial column,’’ and that one of these (form- 
ing part of the so-called ‘‘ Albirupean”’ series) was almost unquestionably 
Paleozoic. At least, this position was indicated by the brachiopod and 
crinoid impressions which are seen on some of the rock fragments exhib- 
ited before the Society. Neither of these impressions is very distinct, but 
such relationship as they indicate is more nearly with Paleozoic than 
with Mesozoic forms. Referring to the formations characterized by Dr. 
Uhler as ‘‘Baltimorean’’? and ‘‘Albirupean,’’ and the ‘‘Potomac’’ of 
the United States Geologists—the last supposed to be in part synchronous 
with the preceding—and to the determination of their age as Jurassic, 
Jurasso-Cretaceous, and Lower Cretaceous (Wealden), Professor Heilprin 
stated that he failed to find any satisfactory evidence proving the strata 
characterized to be older than Upper Cretaceous, and that in all probabil- 
ity they are the absolute representatives or equivalents of a portion of the 
well-known New Jersey series—the colored clays and sands abutting 
upon the Delaware river. 
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