Geos Cascaded Union

std::vector<geos::geom::Polygon*> geomCollection;

  QList<FeatureLayer>::ConstIterator FeatureListEnd = mFeatureList1.end();
  for ( it = mFeatureList1.begin(); it != FeatureListEnd; ++it )
  {
    g1 = it->feature.geometry();
    const std::string wkt = g1->exportToWkt().toStdString();
    geos::geom::Polygon* geom =  dynamic_cast<geos::geom::Polygon*>(geos::io::WKTReader().read(wkt)); //error is here....
    geomCollection.push_back(geom);
  }

  geos::geom::Geometry* unionedPoly = geos::operation::geounion::CascadedPolygonUnion::Union(&geomCollection);


Error
/home/vinayan/QgisGitWorking/Quantum-GIS/src/plugins/topology/topolTest.cpp:746: error: cannot dynamic_cast ‘geos::io::WKTReader().geos::io::WKTReader::read((* & wkt))’ (of type ‘struct geos::geom::Geometry*’) to type ‘struct geos::geom::Polygon*’ (target is not pointer or reference to complete type)