Pope Francis on Tuesday praised the indigenous tradition of showing great respect for elders and learning from them, saying their memory must not be lost in modern society's "fog of forgetfulness."

Francis is on a week-long tour of Canada to apologize for the Roman Catholic Church's role in running residential schools that tore indigenous children away from their families and became places where abuse was rampant.

His words were particularly poignant for indigenous communities because the residential schools, which ran from 1870 to 1996, destroyed the link between generations so precious to indigenous cultures.

He presided over the Mass while seated because of a knee ailment and in his homily hoped for "a future in which the history of violence and marginalization suffered by our indigenous brothers and sisters is never repeated."

The Mass at Edmonton's Commonwealth Stadium was held a day after the pope travelled to the town of Maskwacis, site of two former schools, and issued a historic apology that called the Church's role in schools and the forced cultural assimilation they attempted a "deplorable evil" and "disastrous error". [L1N2Z61KG].

About 50,000 people attended the service, which took place on the day the Roman Catholic Church marks the feast of the grandparents of Jesus. Francis, who has often spoken about what he learned from his grandmother Rosa in Buenos Aires, used the occasion to repeat his frequent appeals to younger generations to cherish their grandparents and learn from them.

Francis called grandparents "a precious treasure that preserves a history greater than themselves". He said modern society should be more attuned to the gifts of elders, who should not be pushed aside simply because they could not be as productive as before.

"In the fog of forgetfulness that overshadows our turbulent times, it is essential to cultivate our roots, to pray for and with our forebears, to dedicate time to remember and guard their legacy. This is how a family tree grows; this is how the future is built."

NEVER FORGET, BUT FORGIVE

Francis entered the stadium standing in a popemobile, which stopped frequently as it toured the pitch so babies and children could be brought to him to kiss or bless.

Before the pope arrived, Phil Fontaine, a former Assembly of First Nations National Chief and a residential school survivor, reflected on Francis's visit on Monday to Maskwacis.

"I want to say to you my friends that what we really are talking about is forgiveness. We will never reach reconciliation without forgiveness," Fontaine said.

"We will never forget but we must forgive. We invite the Catholic Church to rebuild the fractured relationship it had with us, for us and for all Canadians."

Fontaine was among the indigenous leaders who met the pope at the Vatican earlier this year and invited him to Canada.

In the afternoon, Francis is due to visit Lac Ste. Anne, a pilgrimage site about 70 km (44 miles) west of Edmonton popular with both indigenous Canadian Catholics and those of European origin.

More than 150,000 indigenous children were separated from their families and brought to residential schools over the years. Many were starved, beaten for speaking their native languages and sexually abused in a system that Canada's Truth and Reconciliation Commission called "cultural genocide."

Indigenous leaders as well as survivors of the schools said that while the pope's apology on Monday evoked strong emotions and was a highly significant step towards reconciliation, more action needed to be taken by the Church and the government.

"You can't just say, 'I am sorry,' and walk away. There has to be effort, and there has to be work in more meaningful actions behind words," said Nakota Sioux Nation Chief Tony Alexis.

On Wednesday, the pope will travel to Quebec City for the more institutional part of his visit, meeting with government officials and diplomats.

On his way back to Rome on Friday, he will stop for a few hours in Iqaluit in the Canadian Arctic, where indigenous affairs will return to the fore.

The Iqaluit area is one of the fastest-warming parts of North America and there the pope is expected to address the dangers of climate change.