The Figuera Lava, the oldest stratigraphic unit now recognized in northeastern Puerto Rico, and the overlying Fajardo Formation are redescribed and the name Figuera redefined and reinstated for formal use. Previously, lower Tertiary strata some distance from the type areas of the Figuera and Fajardo were correlated with the units by reconnaissance. Recent detailed mapping and paleontology now p...

The purpose of this article is to analyze several Lie algebras associated to " orbit configuration spaces " obtained from a group G acting freely, and properly discontinuously on the upper 1/2-plane À 2. The Lie algebra obtained from the descending central series for the associated fundamental group is shown to be isomorphic, up to a regrading, to 1. the Lie algebra obtained from the higher hom...

The class of nilpotent groups of class c and prime exponent p> c with additional predicates Pc ⊆Pc−1 ⊆ . . . ⊆P1 for suitable subgroups has the amalgamation property. Hence the Fräıssé limit D of the finite groups of this class exists. 〈1〉⊆Pc(D)⊆ . . . ⊆P2(D)⊆P1(D)=D is the lower and the upper central series of D. In this extended language, D is ultrahomogeneous. The elementary theory of D allo...