-12 The American Geologist. March, issu 
Many of the rocks contain distinctive faunas and numerous discover- 
ies of fossils have been made throughout the belt. 
Besides the great unconformity there are many overlaps and local 
unconformities of considerable extent, of which the greatest is at the 
base of the Green Pond conglomerate. 
The Skunnemunk conglomerate caps the double summit of Skunne- 
munk mountain and extends along the western side of Bellvale and 
Bearport mountains. The Bellvale flagstones constitute the greater 
part of Skunnemunk mountain, the northern and eastern portions of 
Bellvale and Bearport mountain, and the region about Clinton Falls. 
Along the western side of Bearport mountain they are in greater part 
cut out by the fault above mentioned. The Monroe shales extend along 
the slopes and valleys adjoining the ridges of Bellvale tiag6, and south- 
ward up the Longwood valley. They are everywhere very fossiliferous. 
The Oriskany quartzites and white conglomerates occur in limited 
areas, but are exposed at many points from the Longwood valley to the 
vicinity of Cornwall station, New York. The Helderberg limestone 
occurs with the Oriskany and contains typical fossils. It is nearly every- 
where underlain by the Longwood red shales. 
The Green Pond conglomerate constitutes Green Pond, Copperas. 
Kanouse and Bowling Green mountains in New Jersey and the two 
Pine hills in New York. As it overlies the Hudson shales, and is inti- 
mately associated with the red shales and Helderberg limestone, in con- 
formable sequence, there is no doubt as to its Upper Silurian horizon. 
The Hudson formation occurs in very restricted areas within this 
belt, but covers a wide area to the northwest in Orange county. It lies 
unconformably on the Cambrian limestones. These limestones under- 
lie a considerable portion of the belt and outcrop at many points along 
its margin. Their erosion gave rise to the basin in which the forma- 
tions of the belt were deposited. As has long been known, the lime- 
stones are underlain by a quartzite and conglomerate at the head of 
Macopin pond in New Jersey. 
33. A prismatic stadia telescope. Robert H. Richards, Boston, Mass. 
(Introduced by Prof. W. H. Niles.) This instrument may be used for 
measuring distances from the hand or from a tripod. From the hand 
comparatively short distances only can be measured, with self-reading 
target. 400 feet; tape target, 1,000 feet. From a tripod, 2,000, 3000 and 
even 5,000 feet may be measured, according to the magnifying power of 
the telescope, with an error not exceeding 0.1 per cent., and if the mean 
of several observations is taken, with an error probably not exceeding 
.04 per cent. 
.'»'/'. Ancient volcanic rocks along the eastern border of North Amer- 
ica. George H. Williams; Baltimore, Md. The occurrence of ancient 
volcanic rocks at various horizons along the Appalachian belt has long 
been recognized by some American geologists. It was the object of 
this paper to direct attention to many newly discovered areas of this 
character, as well as to summarize and co-ordinate all pre-existing in- 
formation on the subject. For this purpose the views held in other 
countries regarding volcanoes were stated, and the frequent misinterpre- 
tation of such rocks in this country was mentioned. The criteria for 
the recognition of ancient and altered volcanic materials were then 
given, including the features which distinguish them from other igne- 
ous, as well as from sedimentary rocks. All existing knowledge regard- 
ing the occurrence of such rocks in eastern North America was then 
summarized, beginning with Newfoundland and passing southwest. 
This summary 'is based upon: 1, published literature; 2, unpublished 
notes or observations by others; 3. extended personal observations by 
the writer. It is hoped that a definite formulation of the problem in 
