Changes

==G. prisca==

==G. prisca==

''G. prisca'' is well known from the Ordovician (and is thus a useful age marker), but the gas chromatographic characteristics of ''G. prisca'' or its descendants have been seen in rocks as young as Devonian. In some studies of the Michigan basin, a few of which predated the recognition of the geochemical peculiarities of ''G. prisca'', several workers mistook the presence of ''G. prisca''-like chromatographic characteristics in the Devonian oils as absolute indicators of an Ordovician source. In fact, some of the Devonian source rocks themselves show the same characteristics (D. Waples, unpublished data).

''G. prisca'' is well known from the Ordovician (and is thus a useful age marker), but the gas chromatographic characteristics of ''G. prisca'' or its descendants have been seen in rocks as young as [[Devonian]]. In some studies of the Michigan Basin, a few of which predated the recognition of the geochemical peculiarities of ''G. prisca'', several workers mistook the presence of ''G. prisca''-like chromatographic characteristics in the Devonian oils as absolute indicators of an Ordovician source. In fact, some of the Devonian source rocks themselves show the same characteristics (D. Waples, unpublished data).

==X-compounds==

==X-compounds==